The construction industry is increasing realizing that specifications are an essential part of describing design. Some aspects of construction are more efficiently described in words than by a multitude of larg scale drawings. Specifications have to be correct and clear to the design teams that are using them. This text, which is non-specific to any particular model specification, describes all the tests and standards necessary to achieve these aims. It discusses how to write a good specification when using a model, how to write a good specification when not doing so, and how to build a model specification. The author explains the present variety of different practices in construction documentation in such a way that they do not detract from sound specification writing principles.