Supersymmetric Wilson loops
  I construct 1/16, 1/8 and 1/4 BPS Wilson loops in N=4 supersymmetric Yang-Mills theory and argue that expectation values of 1/4 BPS loops do not receive quantum corrections. At strong coupling, non-renormalization of supersymmetric Wilson loops implies subtle cancellations in the partition function of the AdS string with special boundary conditions. The cancellations are shown to occur in the semiclassical approximation. 
K. Zarembo