Piecewise Constant Fitting, a family of algorithms for segmentation of DNA copy number data from microarray experiments or DNA sequencing. The sensitivity of the algorithms are controlled by a single parameter (called gamma) for which useful default values are available for most platforms. The resulting segmentation will be statistically optimal in a least squares sense, conditionally on the number of breakpoints found. The algorithms cover (1) segmentation of one or more samples individually, (2) joint segmentation of multiple samples to find a set of common breakpoints, and (3) segmentation of SNP-array data with two measurement tracks (LRR and BAF). All algorithms are freely available in the R package Copynumber; see Gro Nilsen et al (BMC Genomics, 2012) for details.