One of his books is called A Timeless Way of Building. There is a Wikipedia entry on it HERE.
In this book Alexander sets out to describe the perfection of use to which buildings could aspire:
Alexander uses a concept which he calls the "quality without a name", and argues that we should seek to include this nameless quality in our buildings.
"The first place I think of when I try to tell someone about this quality is a corner of an English country garden where a peach tree grows against a wall. The wall runs east to west; the peach tree grows flat against the southern side. The sun shines on the tree and, as it warms the bricks behind the tree, the warm bricks themselves warm the peaches on the tree. It has a slightly dozy quality. The tree, carefully tied to grow flat against the wall; warming the bricks; the peaches growing in the sun; the wild grass growing around the roots of the tree, in the angle where the earth and roots and wall all meet.This quality is the most fundamental quality there is in anything."
Also of note is the design of the book, it is a long series of italicized headlines that are followed by short sections that provide more detail. The author suggests that this long book (over 500 pages) can be read in an hour by only reading the italicised headlines, which frame the book's complete argument.
Alexander also published two follow on volumes on architecture that for a trilogy with this book - A Pattern Language: Towns, Buildings, Construction and The Oregon Experiment.
The Pattern Language book has been very influential in computer science and software engineering (for example HERE).
