We describe the open-source global fitting package GAMBIT: the Global And
Modular Beyond-the-Standard-Model Inference Tool. GAMBIT combines extensive
calculations of observables and likelihoods in particle and astroparticle
physics with a hierarchical model database, advanced tools for automatically
building analyses of essentially any model, a flexible and powerful system for
interfacing to external codes, a suite of different statistical methods and
parameter scanning algorithms, and a host of other utilities designed to make
scans faster, safer and more easily-extendible than in the past. Here we give a
detailed description of the framework, its design and motivation, and the
current models and other specific components presently implemented in GAMBIT.
Accompanying papers deal with individual modules and present first GAMBIT
results. GAMBIT can be downloaded from gambit.hepforge.org.