When analyzed according to subject matter, there are six separate major categories of writings collected in the Nag Hammadi codices:

Writings of creative and redemptive mythology, including Gnostic alternative versions of creation and salvation:

The Apocryphon of John
The Hypostasis of the Archons
On the Origin of the World
The Apocalypse of Adam
The Paraphrase of Shem.

Observations and commentaries on diverse Gnostic themes, such as the nature of reality, the nature of the soul, the relationship of the soul to the world:

The Gospel of Truth
The Treatise on the Resurrection
The Tripartite Tractate
Eugnostos the Blessed
The Second Treatise of the Great Seth
The Teachings of Silvanus
The Testimony of Truth.

Liturgical and initiatory texts:

The Discourse on the Eighth and Ninth
The Prayer of Thanksgiving
A Valentinian Exposition
The Three Steles of Seth
The Prayer of the Apostle Paul
The Gospel of Philip

listed under the sixth category below, has great relevance here also, for it is in effect a treatise on Gnostic sacramental theology).

Writings dealing primarily with the feminine deific and spiritual principle, particularly with the Divine Sophia:

The Thunder, Perfect Mind
The Thought of Norea
The Sophia of Jesus Christ
The Exegesis on the Soul

Writings pertaining to the lives and experiences of some of the apostles:

The Apocalypse of Peter
The Letter of Peter to Philip
The Acts of Peter and the Twelve Apostles
The (First) Apocalypse of James
The (Second) Apocalypse of James
The Apocalypse of Paul

Scriptures which contain sayings of Jesus as well as descriptions of incidents in His life:

The Dialogue of the Saviour
The Book of Thomas the Contender
The Apocryphon of James
The Gospel of Philip
The Gospel of Thomas

This leaves a small number of scriptures of the Nag Hammadi Library which may be called "unclassifiable." It also must be kept in mind that the passage of time and translation into languages very different from the original have rendered many of these scriptures abstruse in style. Some of them are difficult reading, especially for those readers not familiar with Gnostic imagery, nomenclature and the like. Lacunae are also present in most of these scriptures -- in a few of the texts extensive sections have been lost due to age and deterioration of the manuscripts. The most readily comprehensible of the Nag Hammadi scriptures is undoubtedly The Gospel of Thomas, with The Gospel of Philip and the The Gospel of Truth as close seconds in order of easy comprehension. (These texts were all also thankfully very well preserved and have few lacunae.) There are various translations of most of these scriptures available; the most complete being the one volume collection The Nag Hammadi Library in English, edited by James Robinson, from which the translations presented here are principally quoted.