L-series lenses
Top-of-the-line Canon EF lenses are designated as L-series, or "Luxury" lenses.[1] L-series lenses have superior optical performance and are typically built with a solid construction to withstand constant use and harsh conditions. They can be recognized by a red ring around the front part of the lens. Most recent L lenses have sealing to help resist dust and water. L-series lenses are more frequently used by professionals and serious amateurs due to their higher optical quality and better build quality.

An EF lens is designated as an L-series lens only when it contains at least one fluorite or ultra-low dispersion glass element, combined with super-low dispersion glass and ground aspherical elements. There are also some lenses which include one or more of these technologies yet which are not designated as L lenses. L-series lenses are also usually equipped with USM (particularly in recent years), IS, or both, but what sets an L-lens apart from the rest is its optical performance and its build quality. There are also several EF-S lenses which have similar or even better optical performance than Canon L-lenses, however due to the large number of professionals who use full-frame format Canon cameras (and the lack of 'L' quality build on the EF-S range), it is unlikely EF-S lenses will be labeled professional L-series lenses in the near future.