A modular side rail and removable step system for a vehicle is disclosed. In one aspect, the kit includes first, second, and third removable steps that may be mounted to the side rail. In one aspect, the side rail main body has a channel-shape defining a longitudinal opening between an adjacent first side and an adjacent second side. A plurality of step attachment arrangements may be provided on the first side of the side rail main body to allow the first, second, and third steps to be mounted to the side rail main body in various configurations. For example the plurality of step attachment arrangements may be arranged and configured to provide attachment locations for mounting the first and third removable steps in a first step assembly configuration and for mounting the second removable step in a second step assembly configuration.