Muddy coasts are land-sea transitional environments common along low-energy shorelines around the world. They exist in climatic settings and tidal regimes ranging from microtidal to macro-tidal. Climatic warming and relative sea level rise are likely to have a greater impact on low-lying muddy coasts and deltas than most other coastal environments. This was the working hypothesis of the Scientific Committee on Oceanic Research (SCOR) Working Group 106, “Relative Sea Level and Muddy Coasts of the World,” which concluded its deliberations in the late 1990s.