Heat lines and mass lines are well established as powerful tools for visualization and analysis of two-dimensional convective heat and/or mass transfer. These tools were proposed in the eighties, and their use and range of use in the field of convective heat and/or mass transfer have grown since they were proposed. In this work, a new field based on the momentum functions and momentum lines is proposed for steady flow visualization and analysis. As momentum is a vector entity, two momentum functions need to be defined and evaluated, one for each momentum component. The contour plots of the momentum functions, the momentum lines, are the useful tools for flow visualization and analysis. Additionally, momentum arrows can also be used for visualization purposes. Such tools provide a clear physical insight about the momentum transfer in flows, and important information concerning the forces between the fluid and the solid walls interacting with it. Some illustrative examples are presented in order to show the usefulness of the momentum lines for flow visualization and analysis. © 2005 Elsevier Ltd. All rights reserved.