Provided are anti-PD-L1 antibodies or fragments thereof. The antibodies orfragments thereof specifically bind to theimmunoglobulin C domain of the PD-L1 protein. In various example, theantibodies or fragments thereof include a VH CDR1 of SEQID NO: 1, a VH CDR2 of SEQ ID NO: 2, a VH CDR3 of SEQ ID NO: 3, a VL CDR1 ofSEQ ID NO: 4, a VL CDR2 of SEQ ID NO: 5,and a VL CDR3 of SEQ ID NO: 6, or variants of each thereof. Methods of usingthe antibodies or fragments thereof for treating anddiagnosing diseases such as cancer and infectious diseases are also provided.