What is the difference between polyclonal and monoclonal antibodies?

Monoclonal antibodies bind to one unique epitope on an antigen, while polyclonal antibodies bind to more than one type of epitope on an antigen. This occurs because monoclonal antibodies are produced by the same clone of plasma B cells, making the antibody population homogenous. Polyclonal antibodies have a heterogenous antibody population since they are produced by different clones of plasma B cells. While monoclonal antibodies tend to have lower cross-reactivity and produce lower background than polyclonal antibodies, the higher overall affinity and sensitivity of polyclonal antibodies can be beneficial when detecting low quantities of protein.