Fluorescence techniques are extremely powerful tools for probing the structure and function of biomolecules. In particular, the use of fluorescence resonance energy transfer (FRET) is becoming increasingly important as a "molecular ruler", providing information on interactions at the nanoscale. FRET involves an excited fluorescent donor molecule transferring it's excess energy to an acceptor molecule: the efficiency of this energy transfer process depends upon the distance between the donor and acceptor. Time-resolved fluorescence measurements offer the most sensitive and informative study of the FRET process. By performing the measurement under a microscope, any spatial variations in lifetime within a sample can be resolved. This work is concerned with fundamental characterisation of time-resolved FRET within biomolecules and the development of the emerging technique of fluorescence lifetime imaging microscopy (FLIM) for combined FLIM-FRET studies.