The invention provides 4-amino-4-oxobutanoyl peptides of Formula I and the pharmaceutically salts and hydrates thereof. The variables R, R1, R6-R8, R16, R18, R19, M, n, T, Y, and Z are defined herein. Certain compounds of Formula I are useful as antiviral agents. The 4-amino-4-oxobutanoyl peptides disclosed herein are potent and/or selective inhibitors of viral replication, particularly Hepatitis C virus replication. The invention also provides pharmaceutical compositions containing one or more 4-amino-4-oxobutanoyl peptides and one or more pharmaceutically acceptable carriers. Such pharmaceutical compositions may contain a 4-amino-4-oxobutanoyl peptides as the only active agent or may contain a combination of a 4-amino-4-oxobutanoyl peptides and one or more other pharmaceutically active agents. The invention also provides methods for treating viral infections, including Hepatitis C infections.