Classical commentaries study each psalm on its own. However, there is a growing trend to look at the composition of the Psalter. The present commentary on the fifth and last "book" of psalms (Ps 107-150) carries out a systematic analysis of the composition of this set of forty-four psalms, at all levels of its organization: first each psalm on its own, followed by each subsequence formed of several psalms, then each sequence, each of the five subsections that constitute the fifth book, and finally the whole section, i.e., the book. The last five psalms (146-150) are, so to speak, outside the system, for they constitute the doxology that concludes not only the fifth book but also the entire Psalter. The composition is extremely elaborate. At the centre of the construction, Ps 119 which is a long meditation on the Law. It is preceded by the "Egyptian Hallel" which celebrates the exodus from the land of slavery (Ps 113-118) and followed by the "Psalms of Ascents" which sing and hope for the return from exile in Babylon (Ps 120-134). Finally, at the extremities, two subsections that correspond to each other: in the psalmist's own words, "From the mouth of deceit to the thanksgiving of the righteous" (Ps 107-112), "From the venom of the serpent to the praise of the righteous" (Ps 135-145). The interpretation of each group of psalms allows us to reach a greater meaning, which clearly exceeds the sum of the interpretations of each of the units that make it up.