This report explores rainfall-runoff models, their generation methods, and the categories under which they fall. Runoff plays an important role in the hydrological cycle by returning excess precipitation to the oceans and controlling how much water flows into stream systems. Modeling runoff can help to understand, control, and monitor the quality and quantity of water resources. A few categories of rainfall-runoff models are described by the model structure and spatial processes within the model. Both control the way models calculate runoff. Model structure is based on the governing equations a model uses to determine runoff; categories can be generalized into empirical, conceptual, and physical structures. Spatial processes within a model are the interpretation of the catchment characteristics to be modeled. This category separates models into lumped, semi-distributed, and distributed models, which is a generalization because many models overlap and contain elements from each of the categories. A discussion about comparing different runoff models and observed runoff values is presented as well. This report aims to inform modelers about various rainfall-runoff models and their strengths and weaknesses.