Provided are anti-human 4-1BB antibodies and fragments thereof with one or more structural features that are not found in a reference anti-human 4-1BB antibody, where said features may improve certain characteristics of the antibody relative to a reference antibody. Various in vitro and in vivo methods and reagents related to anti-human 4-1BB antibodies described herein are also provided. Methods include, for example, inducing T-cell proliferation, inducing T cell secretion of IFNγ, as well as detection, prevention, and/or therapeutic treatment of cancer using an anti-human 4-1BB antibody or fragment thereof.