CASINO is a code for performing quantum Monte Carlo (QMC) electronic structure calculations for finite and periodic systems. Its development was inspired by a Fortran 77 development code (known simply as 'the QMC code') written in the early 1990s in Cambridge by Richard Needs and Guna Rajagopal, assisted by many helpful discussions with Matthew Foulkes. This was later extended by Andrew Williamson up to 1995 and then by Paul Kent and Mike Towler up to 1998. Various different versions of this program were able to treat FCC solids, single atoms and the homogeneous electron gas. By the late 1990s it was clear that a modern, general code capable of treating arbitrary systems (at least atoms, molecules, polymers, slabs, crystals and electron phases) was required, not only for the use of the Cambridge QMC group, but for public distribution. At that time, a sufficiently general, user-friendly, publicly available code did not exist, and it was felt to be a good thing to create one to allow people around the world to join in the fun.

So, beginning in 1999, a new Fortran 90 code - CASINO - was gradually developed in the group of Richard Needs largely by Mike Towler, considerably assisted from 2002 by Neil Drummond and from 2004 by Pablo López Ríos. Some routines from the old code were retained, translated and reused, although most were gradually replaced. The main aims of the new code were generality, speed, ease-of-use and transferability over a wide range of computational hardware. It is hoped that these objectives have largely been attained, but the code continues to be actively developed.