Provided herein are novel anti-CD27 and anti-PD-L1 antibodies, and binding domains thereof, as well as bispecific constructs and anti-CD27 binding domain linked to an anti-PD-L1 binding domain. Also provided herein are methods of stimulating T cell activity, methods of inducing or enhancing an immune response, and methods of treating a disease or condition (e.g., cancer) by administering the bispecific constructs, antibodies, or antigen binding fragments thereof, or compositions described herein to a patient in need thereof.