TLS (translation/libration/screw) models describe rigid-body vibrational motions of arbitrary objects. A single-group TLS model can be used to approximate the vibration of an entire protein molecule within a crystal lattice. More complex TLS models are broadly applicable to describing inter-domain and other internal vibrational modes of proteins. Such models can be derived and refined from crystallographic data, but they can also be used to describe the vibrational modes observed through other physical techniques or derived from molecular dynamics. The use of TLS models for protein motion has been relatively limited, partly because the physical meaning of the refined TLS parameters is not intuitive. Here, a molecular viewer, TLSView, is introduced using OpenGL and based on the mmLib library for describing and manipulating macromolecular structural models. This visualization tool allows an intuitive understanding of the physical significance of TLS models derived from crystallographic or other data and may be used as an interactive tool to display and interpret inter-domain or other motions in protein structural models. TLSView may also be used to prepare, analyze and validate TLS models for crystallographic refinement.