These cross-linking agents contain at least two reactive groups that are reactive towards numerous groups, including sulphydryls, amines and carbohydrates, and create chemical covalent bonds between two or more molecules. Functional groups that can be targeted with cross-linking agents are primary amines, carboxyls, sulfhydryls, carbohydrates and carboxylic acids. Protein molecules have many of these functional groups and therefore proteins and peptides can be readily conjugated using cross-linking agents.

Variety of cross-linking agents, reaction specific buffers and accessories are avialble to perform and facilitate cross-linking applications. These cross-linking agents are divided into groups dependent on the number and similarity of the reactive groups. Photoreactive groups are used when no specific groups are available to react with as photoreactive groups react non-specifically upon exposure to UV light.

These are used for protein structural and functional studies, cell membrane structural studies, protein and receptor interactions, cell surface studies, solid-phase immobilisation, preparation of immunogens, immunotoxins and other conjugated protein reagents, protein to DNA/RNA cross-linking, reactive group transfer, protein-protein conjugation, and for immunological tools.