In a software product family context, software architects design architectures that support product diversification in both space (multiple contexts) and time (changing contexts). Product diversification is based on the concept of variability: a single architecture and a set of components support a family of products. Software product families have to support increasing amounts of variability, but variability dependencies are often ill-defined and have unexpected or even unknown behavior. This paper suggests a (1) taxonomy and a (2) hierarchy of variability dependencies in a software product family context. The taxonomy is based on the concept of variation points and identifies four main types of variability dependencies. The four-tier hierarchy is a generalization of the architectural layers found in the so-called Building Block Method.