What is a good description of C4.5 Decision tree algorithm?

Gregory Piatetsky-Shapiro answers:
The best description is in R. Quinlan book C4.5: programs for machine learning, ISBN:1-55860-238-0, Morgan Kaufmann, 1993.

See also Ross Quinlan personal page which has many of his papers, and

a decision-tree module of my Data Mining Course, at www dot kdnuggets dot com /data_mining_course/dm7-dec-tree-c45.ppt

gioseza adds a warning:
in Quinlan's own words, the pruning strategy used by C4.5 is a "heuristic with questionable underpinnings."

gioseza suggests to study the more statistically grounded approach used by CART.

Note: ID3 (id3) algorithm is a predecessor of C45 algorithm.