The Abhidharmasamuccaya survives in Chinese and Tibetan translations, with a section of the Sanskrit text (approximately two fifths) discovered in Tibet in 1934 by Rāhula Saṅkṛtyayana. In 1950 Pralhad Pradhan produced a reconstructed Sanskrit version of the full text, using the extant Sanskrit section and drawing on the Tibetan to fill in the gaps. In 1971, relying primarily on Pradhan's reconstruction, Walpola Rahula rendered the Abhidharmasamuccaya into French.
Asaṅga, judging from his works, was primarily an Agamist, i.e., one who based himself on the āgamas. This text served as his overview of abhidharma from his developing Yogacaric perspective. The following summary relies primarily on Xuanzang's Chinese rendition (T.31.1605), though I have consulted Rahula for suggestions on Sanskrit equivalents.
The text begins with verses briefly introducing the themes to be taken up:
本事與決擇。 是各有四種。 三法,攝,應,成。
諦, 法, 得, 論議。 幾, 何因, 取, 相。 建立,與次第。
義, 喩, 廣分別。 集總頌應知。
"The main text [i.e., the lakṣaṇa-samuccaya, collection of characteristics] and the expository section [i.e., the viniścaya-samuccaya, collection of explanations] each have four parts.
"[The four parts of the main text are] the Three Dharmas [viz., skandhas, dhātus, āyatanas]; categories (saṃgraha); association (samprayoga); and accomplishments (samanvāgama).
"[The four parts of the exposition are] the truths (satya), doctrine (Dharma), [karmic] accrual (prapti), and rhetorical skill (sāṃkathya).
"How many? For what reason? Appropriation (upādāya); Characteristics (lakṣaṇa); Definitions (vyavasthāna); And gradations (anukrama), referents (artha), examples (dṛṣṭanta), and broadening differentiations (prabheda),
all this the Samuccaya makes known."
In the first three fascicles the Three Dharmas (viz. the five skandhas, eighteen dhātus, and twelve āyatanas) are discussed. For instance, after enumerating the items in each of the Three Dharmas, he takes up the "How much?" question:
Why are there only five skandhas? Because these are the five ways in which the notion of self appears (為顯五種我事故). This means, body as the concrete self (謂身\具我事), pain/pleasure (vedanā) as the function of self (受用我事), language as the explainer of self (言說我事), the construction of all dharmas and non-dharmas as [performed by] the self (造作一切法非法我事)﹔ and that on which all those are fixed is the self's self-nature (彼所依止我自體事).
After taking up similar questions for the dhātus and āyatanas, he turns to the "For what reason" question:
For what reason are the skandhas-of-appropriation (取蘊 upādāna-skandha) called "upādāna" (appropriation)? ... they are appropriation. That means the skandhas contain desire (欲 chanda) and appropriational intent (貪 rāga). For what reason are desire and appropriational intent called "upādāna"? Since the ability of present skandhas to lead to future skandhas is not cut off, they subtly desire the future while remaining attached to present skandhas, and are thus called upādāna.
In this way he takes up all Three Dharmas. For instance, to the question, "what is the characteristic of rūpa (sensate form)?" he answers:
Change is the characteristic of rūpa. There are two types: Change as temporary resistance in sensory contact (sparśa) (觸對變壞) and change in terms of appearing in a locus (方所示現). What is change in terms of sensory contact? It is change caused when there is sensory contact with a hand, foot, stone, clump, blade, stick, cold, heat, hunger, thirst, mosquito, gadfly, snake, scorpion, etc. What is change in terms of appearing in a locus? Characteristics appear in space in such or such a form, or in such or such a form; sometimes they are definite in the mind, sometimes indefinite [in which case] one investigates their association with the other things in which they are situated.
In this manner Asaṅga treats the Three Dharmas in detail, analyzing them in terms of substance and name, saṃvṛti and paramārtha, conditioned and unconditioned, mundane and transmundane, time and space, conditioned co-arising, and so on, demonstrating that no self occurs in any of these.
In Xuanzang's translation this continues into the third fascicle, which also includes three short chapters, the first dealing with categories (攝 saṃgraha), eleven to be exact: 1. characteristics (相 lakṣaṇa), 2. dhātus 界, 3. species (種類 jāti), 4. situation (分位 avasthā), 5. accompaniments (伴 sahāya), 6. space (方 deśa), 7. time (時 kāla), 8. part (一分 ekadeśa), 9. whole (具分 sakala), 10. mutuality (更互 anyonya), 11. paramārtha 勝義.
In the next short chapter Asaṅga discusses associations (相應 samprayoga), specifically citta and caittas (心心所) which are citta samprayukta dharmas (心相應法).
The final chapter of the third fascicle, on accomplishments (成就 samanvāgama), discusses how the seeds (種子 bījās) of sentient beings affect their station in the triple world (desire, form and formless) according to the mundane and transmundane qualities they cultivate; by understanding this, one overcomes attachment and aversion.
Fascicles four to six deal with the Four Noble Truths:
The first Truth: Suffering (duḥkha) encompasses all sentient beings, including hell denizens, animals, hungry ghosts, humans (in various realms), devas (in the Assembly of the Four Great Kings, the Heaven of Thirty-three, Yama's realm, etc.), and inhabitants of the various Brahmalokas (Asaṅga provides a detailed inventory of Buddhist cosmology). Even the insentient worlds are subject to suffering, since they are impermanent, undergoing unending change and dissolution.
The famous formula of the eight examples of suffering (birth, old age, sickness, death, acquiring something unpleasant, loss of something pleasant, not attaining what one desires, the very fact that the five appropriational skandhas are suffering) is analyzed in terms of three kinds of duḥkha:
1. duḥkha-duḥkhatā, i.e., ordinary suffering; pain, misery, etc.
2. parināṃa-duḥkhatā, i.e., suffering due to change, instability, impermanence
3. saṃskāra-duḥkhatā, i.e., suffering due to embodied conditioning resulting from previous experiences.
All things are characterised as impermanent (anitya), suffering, empty (śūnya), and non-self (anātman). Rūpa is momentary (rūpasya kṣaṇikatā); atoms lack physical dimension (i.e., extension, niḥśurīra), and are merely a product of analytic speculation. Asaṅga also discusses intermediate states (between lives) (antarābhava) and gandharvas (celestial beings) in the context of death.
The second Truth: The cause of the Arising of Suffering (samudaya) is initially identified by Asaṅga as desire (tṛṣṇā), but he quickly moves on to a more nuanced discussion of kleśa as kleśa-adhipateya-karma (actions permeated by mental disturbances). There follows a detailed analysis of types of kleśa, types of karma, causes of rebirth and conditioning (saṃskāra).
The third Truth: Nirodha (cessation of suffering) is treated in twelve aspects:
1. characteristics (相 lakṣaṇa) - the nonarising of kleśa in the noble path of suchness (真如 tathatā)...
The World Honored One said that "it is the definitive cessation of name-and-form (nāma-rūpa), without remainder in the sensory spheres (處 āyatana) of eye, ear, nose, tongue, body, and mental organ (意 manas)." He also said that "you should now contemplate that in that sphere the eye utterly ceases and the perception of visible forms is detached (遠離) ... up to... the mental organ ceases and the perception of mental objects is detached. For this reason, in suchness (tathatā) objects (ālambana...viṣaya) appear and the contaminated dharmas (sāsrava-dharma) cease. This is the definition (lakṣaṇa) of the truth of cessation (由此道理 顯示所緣 真如境上 有漏法滅 是滅諦相). "
2. depth (甚深 gāmbhīrya) - cessation by putting saṃskāras to rest (saṃskāra-upaśama). Beyond prapañca (proliferation of psycho-linguistic conceptuality).
3. conventional (世俗 saṃvṛti) - cessation attained by suppressing the seeds through the mundane path (laukika-mārga), called 'partial nirvana' (tadāṃśika-nirvāṇa).
4. ultimate (勝義 paramārtha) - complete extirpation of the root seeds (bījānirmūlana) by Noble Insight (ārya-prajñā).
5. incomplete (不圓滿 aparipūri) - cesstion of Śaiṣikas (those still in training), such as Stream-Enterers, Once-Returners, and Non-Returners.
6. complete (圓滿 paripūri) - cessation of Aśaikṣas (those who no longer need to study), comparable to the Arhat fruit.
7. nonadorned (無莊嚴 niralaṃkāra) - cessation of the arhats liberated by insight (prajñā-vimukta)
8. adorned (莊嚴 alaṃkāra) - cessation of the Arhats who possess the three vidyās and six abhijñās.
9. residual (有餘 śeṣa) - cessation (i.e., Nirvana) with remainder
10. nonresidual (無餘 aśeṣa) - cessation without remainder
11. supremacy (最勝 agra) - the cessation of Buddhas and Bodhisttvas, the nonabiding Nirvana
12. synonyms (差別 paryāya) - total cutting off (aśeṣaprahāna), complete renunciation (pratiniḥsarga), final attainment (vyantībhāva), used up (kṣaya), detachment (virāga), cessation (nirodha), tranquility (vyupaśama), etc.
The fourth Truth: Asaṅga provides a detailed listing and discussion of the path/method (mārga), which he breaks into five stages:
1. Sambhāra-mārga 資糧道 (stocking up on provisions for the Path). The Bodhisattva begins on the path to Unexcelled Awakening by practicing śīla, learning to control his senses, etc.
2. Prayoga-mārga 加行道 (Experimenting on the path). The Bodhisattva further develops what he began in the Sambhāra-mārga.
3. Darśana-mārga 見道 (path/method of vision).
In brief, this is the first dharma that immediately follows the mundane path, the inconceivable samādhi prajñā (無所得三摩地鉢羅若) and the dharmas associated with it. Again, its characteristic is cognition in which the objective and subjective supports (ālambyālambana-jñāna) are thoroughly equalized (平等平等智為其相). Again, devoid of each separate sentient being, provisional dharma, and provisional designations entirely, it cognizes devoid of the two provisional ālambana dharmas (i.e., objective and subjective cognitive supports); that is its characteristic...
The Darśana-mārga quickly diversifies into sixteen types. Asaṅga then enters into a detailed excursus on components of the path (with extensive quotes from the Āgamas), defining carefully such terms as vyavasthāna, anubhāva, kṣanti, paripūri, etc.
4. Bhāvanā-mārga 修道 (path/method of mental cultivation)
Above the Darśana-mārga, consisting of the mundane path (世閒道 laukika-mārga), the transmundane path (出閒道 lokuttara-mārga), the weak path (輭道 mṛda-mārga), the medium path (中道 madhyama-mārga), the intense path (上道 adhimātra-mārga), the experimental path (加行道 prayoga-mārga), the path of immediate succession (無閒道 ānantarya-mārga), the path of liberation (解脫道 vimukti-mārga), and the distinct path (勝進道 viśeṣa-mārga).
Asaṅga now dives into an even lengthier discussion of such notions as laukika- and lokottara-mārga, saṃkleśa, vyavadāna, samāpatti, saṃjñā-karaṇa-vyavasthāna, vimukti-mārga, etc., including a minute and original presentation of the 37 bodhipakṣa-dharmas (factors of enlightenment), as well as varieties of meditation.
5. Niṣṭhā-mārga 究竟道 (end of the path) occurs in the eighth bhūmi (Bodhisattva stage), resultant on attaining the vajropamasamādhi (diamond-like samādhi). He discusses topics such as the ten qualities of the aśaikṣa(one no longer requiring training), saṃyoga, visṃyoga, āśraya-paravṛtti, etc.
The next fascicle, Dharma-viniścaya 法品, focuses on the Awakening of the Buddha in terms of the twelve divisions of the Scriptures (十二分聖教 dvādaśāṅga).
The Twelve Divisions of the Scriptures are:
1. sūtra 契經﹔
2. verse narration (應頌 geya) ;
3. exposition (記[竹+別] vyākaraṇa);
4. stanzas (諷頌 gāthā);
5. solemn expression (自說 udana);
6. situations (緣起 nidāna);
7. legends (譬喻 avadāna);
8. original occasions (本事 itivṛttaka);
9. rebirth stories (本生 jātaka);
10. expansive (方廣 vaipulya);
11. miraculous tales (希法 adbhuta-dharma);
12. Didactic (論議 upadeśa).
In the ensuing discussion Asaṅga addresses such questions as "Why did the Tathāgata establish a triple canon?" Answer:
The Sutra piṭaka was established so as to counteract the minor kleśa (upakleśa) of doubt. The Vinaya piṭaka was established so as to counteract the minor kleśa of attachment to the two extremes (of pain and pleasure). The Abhidharma piṭaka was established so as to counteract the minor kleśa of attachment to one's own views. Furthermore, the Sutra piṭaka was established in order to reveal the three disciplines (i.e., śīla, samādhi, prajñā). The Vinaya piṭaka was established for the purpose of accomplishing the disciplines of the higher discipline (adhi-śīla) and for the development of higher mental [abilities] (adhicitta). The Abhidharma was postulated in order to accomplish the discipline of higher wisdom (adhi-prajñā)....
and so on. An interesting hermeneutic theory of text is contained in this section. Sutras, etc., are described in terms of their ālambana (所緣), their ākāra (行相), their āśraya (所依), and their associations (samprayoga 相應). For instance:
It says in a Sutra, "mind and its associates (citta-caitta 心心所法) have ālambana (objective support), ākāra (functional aspects), āśraya (basis), and associations."
In this Dharma (concerning scriptures), what are their ālambanas? It is the Sutras, etc.
What are their ākāra? It is the skandhas, etc., and what is associated with those referents (義 artha).
What is their āśraya? It is communicative indications from others (他表了 para-vijñapti), memory (億念 smṛti), and habituated impressions (習氣 vāsanā).
What are their associates? The ālambana (i.e, the texts) and ākāra (i.e., what one mentally and bodily brings to the text) mutually assist each other to be equally understood.
And so on. Why and how we investigate dharmas is analyzed, neatly broken down into sets of four. For instance, there are four reasons for exploring dharmas: 1. dependence, 2. cause and effect, 3. the evidence of the senses, 4. dharmatā 法爾 ...
What is the Dharmatā reason (法爾道理)? This means that from beginningless time the own-characteristic (自相 svalakṣaṇa) and general characteristic (共相 samanya-lakṣaṇa) that have abided, joined (成就 yukta), in dharmas are Dharmatā (法性法爾). That is diligently contemplating dharmas.
... There are four types of investigations (尋思) of dharmas. 1. Investigating names (名尋思 nāma-paryeṣanā); 2. Investigating things (事尋思 vastu-paryeṣanā); 3. Investigating heuristic self-nature (自體假立尋思 svabhāva-prajñapti-paryeṣanā); 4. Investigating heuristic differentiations (差別假立尋思 viśeṣa-prajñapti-paryeṣanā).
Which Asaṅga goes on to further subdivide and define.
The next chapter, 得品 Prāpti-viniścaya (on karmic accrual), lays itself out primarily in sets of seven, first dealing with defining what a person (補特伽羅 pudgala-vyavasthāna) is, and then defining understanding (建立現觀 abhisamaya-vyavasthāna). Pudgala is viewed in terms of seven categories (primarily with an eye to issues of liberation and attaining the fruit of the path), which are then further broken down. Understanding is distinguished into ten categories (basically in terms of levels affecting liberation and attainment of the fruit, such as understanding which ends one's coursing in saṃsāra, or the difference between the understanding of a Buddha and that of a Bodhisattvas, etc.), which are then explored in some detail.
The final chapter, 論議品 Sāmkathya-viniścaya (On rhetoric), is a debate manual, representing the Buddhist use and evaluation of positions prior to the advent of Buddhist logic a century of so later. Rāhula efficiently summarizes the contents of this chapter thus (p. xx; my translation from the French):
Chapter IV [of this part], entitled "Decisions on Dialectic", treats 1. methods for deciding the meaning (arthaviniścaya), 2. methods for explicating a sutra (vyākhāviniścaya), 3. methods of analytic demonstration (prabhidyasandarśanaviniścaya), 4. methods for treating questions (sampraśnaviniścaya), 5. methods for deciding among groups (saṃgrāhaviniścaya), 6. methods for deciding on the subject matter or controversy (vādaviniścaya), and 7. methods for deciding on the profound and secret meaning of certain passages in the sutras (abhisandhiviniścaya).
This section on vāda (art of debate) by Asaṅga may be considered the first essay on the Buddhist logic that Diṅnāga and Dharmakīrti came to systematize, develop, and perfect later. This subject is treated under seven rubrics: 1. debate or discussion (vāda), 2. assembling a discussion (vādādhikaraṇa), 3. subject of discussion (sādhya, things to prove, sādhana, proof), 4. ornaments of discussion (erudition, eloquence, etc.)(vādālaṅkāra), 5. defeat in discussion (vādanigraha), 6. leaving the discussion (vādaniḥsaraṇa), 7. useful qualities in a discussion (extensive knowledge, self-confidence, lively mind, etc.)(vāde bahukārā dharmāḥ). Finally citing a passage from the Mahāyānābhidharmasūtra which says that a Bodhisattva shouldn't debate with others for twelve reasons, Asaṅga advises only to engage in debate in order to acquire knowledge for one self, but guard against debating for the mere pleasure of arguing.
Note that even while the Abhidharmasamuccaya is ostensibly on Abhidharma - and it does cover some topics commonly found in Abhidharma literature - Asaṅga's many scriptural citations come primarily from sutra literature, not abhidharma texts, including this last quote mentioned by Rāhula above.
 This plays on the notion of self as 'enjoyer' (bhoktṛ), which, as enjoyer of experience, implies 'the one who experiences,' a common characterization of 'self' in Buddhist and Hindu literature.
 It is interesting that Asaṅga uses "language, words" as a synonym for saṃjñā (associative cognition).
 "Construction of all dharmas and non-dharmas" is also an interesting gloss on saṃskāra (embodied karmic conditioning).
 In other words, taking consciousness (the fifth skandha) as foundational to be the essence of what a 'self' is.
 Rāhula, in the introduction to his translation -- Le Compendium de la Super-Doctrine (Philosophie)(Abhidharmasamuccaya) d'Asaṅga, traduit et annoté par Walpola Rāhula, Paris: École Française D'Extrême-Orient, 1971 , p. xv) claims that this chapter discusses "en esprit seulement (cittamātra)," but the term cittamātra (唯心) per se never occurs in Xuanzang's translation. Where in Rāhula's translation he offers: "Il connait la conjonction et la disjonction des choses qui soillent (sāṃkleśa) et qui puifient (vyāvadānika) telles que les sensations (vedanā), en esprit seulement (cittamātra)." Xuanzang has: 能善了悟唯依止心有受想等染諸法相應不相應義.
 The Cheng weishilun offers a similar argument concerning spatiality (ākāśa).
 Three knowledges, trividyā, viz. knowing one's own past life, knowing others' past lives (and the karmic causes operating in them), and eliminating the āśravas (the fundamental cognitive errors glossed as ignorance). The six Abhijñā are the powers gained from meditative practice in the Formless realm: 1. ability to walk on water, etc.; 2. ability to hear at any distance; 3. ability to read the mind of others; 4-6 are the same as the trividyā.
 The Cheng weishilun presents the same five-step path, deriving it as implicit in the last five verses of Vasubandhu's Triṃsikā.
 The implication of 成就, which implies something brought to completion or perfection, something that has fulfilled itself, suggests that this passage means that it is dharmatā which brings dharmas to actuality qua self-characteristic (what uniquely defines a particular dharma) and general characteristic (definition of a dharma as part of a class of similar things).