Fluorescence spectroscopy has been widely used in the study of the structure and dynamics of molecules in complex systems. Steady-state and time-resolved fluorescence methods are commonly used to gain insight into the chemical surroundings of the fluorophore. This thesis discusses a range of complex systems and phenomena that may fruitfully be examined by means of fluorescence spectroscopy, in particular: steady-state fluorescence, fluorescence quenching, fluorescence lifetime, time-resolved fluorescence anisotropy, fluorescence resonance energy transfer (FRET), and excited-state solvation dynamics. This thesis focuses on the interactions of fluorophores with biologically and environmentally important macromolecules, hydrogen atom transfer in the excited-state of medicinal pigment, and use of fluorescence from tissues for food-safety and disease diagnosis.