This treatise addresses the state-of-the-art in dynamic sealing systems for commercial vehicles. A brief review of different seal types is given and a 12 year literature search is included in the references. The scope of the paper, however, is limited to radial lip and mechanical face seals. The lack of understanding of the sealing mechanism is noted. Also discussed are the effects of various design factors; application factors which need specific attention; materials; testing methods; and the need for realistic standardized tests. Field tests are used as the final approval for seal applications, but qualification tests for the same type of application vary widely. Future work should be directed towards understanding the sealing mechanism.