Since their debut in 1987, snakes (active contour models) have become a standard image analysis technique with several variants now in common use. We present a framework called "United Snakes", which has two key features. First, it unifies the most popular snake variants, including finite difference, B-spline, and Hermite polynomial snakes in a consistent finite element formulation, thus expanding the range of object modeling capabilities within a uniform snake construction process. Second, it embodies the idea that the heretofore presumed competing technique known as "live wire" or "intelligent scissors" is in fact complementary to snakes and that the two techniques can advantageously be combined by introducing an effective hard constraint mechanism. The United Snakes framework amplifies the efficiency and reproducibility of the component techniques, and it offers more flexible interactive control while further minimizing user interactions. We apply United Snakes to several different medical image analysis tasks, including the segmentation of neuronal dendrites in EM images, dynamic chest image analysis, the quantification of growth plates in MR images and the isolation of the breast region in mammograms, demonstrating the generality, accuracy and robustness of the tool.