Chromatin immunoprecipitation (ChIP) uses antibodies to investigate protein-DNA interactions.  First, chromatin (fixed or not) is sheared either mechanically or enzymatically into nucleosome sized fragments. The protein(s) of interest, such as transcription factors or histone modifications, is then selectively immunoprecipitated and the previously protein bound DNA fragments are purified.  Regions in the genome associated with the protein of interest should be enriched. 

There are 2 protocols below, one for native ChIP which uses micrococcal nuclease (MNase) digestion and one for µChIP which utilizes sonication on fixed chromatin.