The Duolink® approach provides new insights into proteins and protein interactions. For the first time, individual proteins, their interactions and modifications, can be localized and accurately and objectively quantified in unmodified cells and tissues. Utilizing only a few cells, sub-cellular events, even transient or weak interactions, are revealed in situ and sub-populations of cells can be differentiated. Each Duolink protein detection kit consists of customizable kit compoments and can be configured to meet specific assay requirements.