System Dynamics provides a suitable framework for modeling diseases that can bring together biological, epidemiological, clinical, and public health issues in a manageable way. In this paper, we discuss models for the development and transmission of parasite-borne diseases which involve a primary host (e.g. a human), a vector(e.g. a mosquito), and a parasite . The models discussed here are being applied to different diseases; this paper will refer primarily to results for filaria. We first examine models for the biology of the disease in a vector and in a host, and for disease transmission between two humans through a vector. We then discuss a model for disease transmission in a population of vectors interacting with a population of hosts. We examine the effect of different control strategies, including preventive measures as well as treatment, and also possible effects of changes in the environment. We point out some of the complexities inherent in the biological processes, and the variability resulting from change in the values of the parameters in the system.