The present invention relates to antigen binding proteins, such as monoclonal antibodies, that specifically bind to and activate human triggering receptor expressed on myeloid cells-2 (TREM2) and pharmaceutical compositions comprising such antigen binding proteins. The agonist antigen binding proteins (e.g. antibodies) of the invention are capable of activating TREM2/DAP12 signaling in myeloid cells in the absence of Fc-mediated cross-linking of the antigen binding proteins. Methods of treating or preventing conditions associated with TREM2 loss of function, such as Alzheimer's disease and multiple sclerosis, using the antigen binding proteins are also described.