The HaloTag® Fluorescent Ligands can carry a variety of functionalities, including fluorescent labels, affinity tags and attachments to a solid phase. The covalent bond forms rapidly under general physiological conditions, is highly specific and essentially irreversible. The HaloTag® Fluorescent Ligands allow researchers to apply the chloroalkane group that HaloTag® protein reacts with to any compound or surface with a compatible chemical group, creating endless possible applications.