Structure and engineering of tandem repeat lectins

•Lectins utilize several strategies for multivalency, resulting in strong avidity for glycoconjugates.•Tandem repeat lectins can be searched for in the structural database UniLectin3D.•Tandem repeat lectins are of high interest for understanding protein evolution and for engineering of "neo-lectins".•β-propeller and β-trefoil lectins have great potential as bio-markers.