The protein-DNA interactions play a crucial role in many cellular processes such as DNA replication, recombination, repair, or gene transcription. Here we describe a chromatin immunoprecipitation (ChIP) technique, a tool for identifying DNA regions, which are in vivo associated with protein of interest. The main steps of ChIP are: fixation, chromatin fragmentation, immunoprecipitation with a specific antibody, and analysis of the immunoprecipitated DNA. Different analytical tools combined with ChIP (ChIP-chip, ChIP-seq) enable researchers to map protein binding in a truly genome-wide manner with high resolution.