The formation of vascular networks is important in many biological processes such as embryonic development, wound healing, and tumor growth. Recently there has been much interest in developing in vitro capillary networks to prevascularize implantable tissues in order to overcome diffusion limitation in the transport of nutrients. The structure and function of the networks is influenced by a number of factors such as the availability of oxygen and nutrients, the properties of the surrounding matrix, and the presence of secondary cell types that secrete growth factors. Varying these conditions in the laboratory results in the formation of in vitro networks that have striking visual differences. We use digital image analysis techniques to obtain robust, quantitative, and sensitive fractal and nonfractal indices to characterize such differences. These indices provide information about different structural aspects of the network, such as its space filling characteristic, spatial uniformity, and distribution of branching points and branch length. They are useful for distinguishing between different experimental conditions and provide away of comparing in vitro and in vivo networks. Thus they can be used to guide experimental design to optimize for a desired endpoint.