Analysis of materials using neutron scattering usually requires thermal and cold neutrons rather than those at the higher energies typically liberated by nuclear reactions. Cold neutrons are particularly useful for studying materials characterised by large dimensions, such as polymers, biological materials, and magnetic materials with complex structures. This publication provides a practical overview of considerations when building a cold neutron source, including neutronics and heat removal, design considerations, materials choices and fabrication methods, safety, and licensing. It also describes some typical project management aspects and a path through the steps from installation, commissioning, benchmarking, into operation and eventual decommissioning. In addition, a section describing recent research and development themes including modern moderator materials, catalysts for para hydrogen production, geometrical optimization, scattering kernels, and recent developments in Monte Carlo codes for modelling and optimization is included. The publication has been written for use by all those involved in a project to build a cold neutron source. The publication also includes five annex articles describing experiences with cold sources at reactor- and accelerator-based neutron sources.