Tetrad IV is a program designed for the specification of causal models. It is specifically designed to search for causal relations, but also offers the possibility to estimate the parameters of a structural equation model. It offers a remarkable graphical user interface, which facilitates building, evaluating, and searching for causal models. The search algorithms make it possible to find alternatives for existing models, as well as to find new models when a theoretical directive is lacking. This is illustrated by the detection of a causal model for longitudinal data, which is a viable alternative for a latent growth model. (Contains 6 figures.)