A pipe coupling. for connecting together the ends of two pipes, the pipe coupling comprising: a tubular casing for fitting around a pipe; tensioning means for tightening the casing around the outer surface of the pipe; and a dynamic axial restraint system comprising at least one resilient gripping ring mounted within the casing for gripping the outer surface of the pipe, wherein the gripping ring comprises: an outer convex surface engaging with an inner surface of the casing and adapted to roll against the inner surface of the casing upon axial loading of the pipe; and an inner gripping surface for engaging the outer surface of the pipe, wherein the inner gripping surface comprises a first annular projection having a gripping edge for engaging with the outer surface of the pipe in an initial position of the gripping ring and a second annular projection having a gripping edge, wherein the second annular projection is axially offset from the first annular projection and adapted such that the gripping edge of the second annular projection is brought into engagement with the outer surface of the pipe upon rolling of the outer surface of the gripping ring against the inner surface of the tubular casing whereby the area of the gripping surface in contact with the pipe increases. a tubular casing for fitting around a pipe; tensioning means for tightening the casing around the outer surface of the pipe; and a dynamic axial restraint system comprising at least one resilient gripping ring mounted within the casing for gripping the outer surface of the pipe, wherein the gripping ring comprises: an outer convex surface engaging with an inner surface of the casing and adapted to roll against the inner surface of the casing upon axial loading of the pipe; and an inner gripping surface for engaging the outer surface of the pipe, wherein the inner gripping surface comprises a first annular projection having a gripping edge for engaging with the outer surface of the pipe in an initial position of the gripping ring and a second annular projection having a gripping edge, wherein the second annular projection is axially offset from the first annular projection and adapted such that the gripping edge of the second annular projection is brought into engagement with the outer surface of the pipe upon rolling of the outer surface of the gripping ring against the inner surface of the tubular casing whereby the area of the gripping surface in contact with the pipe increases. an outer convex surface engaging with an inner surface of the casing and adapted to roll against the inner surface of the casing upon axial loading of the pipe; and an inner gripping surface for engaging the outer surface of the pipe, wherein the inner gripping surface comprises a first annular projection having a gripping edge for engaging with the outer surface of the pipe in an initial position of the gripping ring and a second annular projection having a gripping edge, wherein the second annular projection is axially offset from the first annular projection and adapted such that the gripping edge of the second annular projection is brought into engagement with the outer surface of the pipe upon rolling of the outer surface of the gripping ring against the inner surface of the tubular casing whereby the area of the gripping surface in contact with the pipe increases.