The iFit library (pronounce [eye-fit]) is a set of methods to load, analyze, plot, fit and optimize models, and export results. iFit is based on Matlab, but can also be launched without Matlab license (stand-alone version). It does not currently include advanced graphical user interfaces (GUI), but rather focuses on doing the math right. Any text file can be imported straight away, and a set of binary files are supported. Any data dimensionality can be handled, including event based data sets (even though not all methods do work for these). Any model can be assembled for fitting data sets.