This technical brief summarizes an elegant algebraic description of rigid body position and attitude along with analytical derivatives associated with body motions. The equations presented here offer a fully general representation that is entirely singularity-free. The expressions capture all six degrees of freedom associated to a physical body within a math model containing exactly six free parameters based on the exponential map. A particularly pragmatic benefit is that the math model and all of its parameters have direct associations with physical characteristics that can be observed and/or measured directly by physical instrumentation and sensor systems. The expressions describing body position and attitude are necessarily non-linear, but have relatively simple forms on which simple numerical solution methods are exceptionally effective.