The Variant Call Format (VCF) is a flat-file, tab-delimited textual format intended to concisely describe reference-indexed variations between individuals. VCF provides a common interchange format for the description of variation in individuals and populations of samples, and has become the defacto standard reporting format for a wide array of genomic variant detectors. vcflib provides methods to manipulate and interpret sequence variation as it can be described by VCF. It is both: an API for parsing and operating on records of genomic variation as it can be described by the VCF format and a collection of command-line utilities for executing complex manipulations on VCF files. The API itself provides a quick and extremely permissive method to read and write VCF files. Extensions and applications of the library provided in the included utilities (*.cpp) comprise the vast bulk of the library's utility for most users. WWW: https://github.com/vcflib/vcflib