The investigation of biomolecular recognition via Förster Resonance Energy Transfer (FRET)1 and photoluminescence plays an important role for quantifying concentrations and distances in many fields of the life sciences, analytical chemistry, and biophysics. 2,3 The materials used for FRET are paramount for the success of the analytical application, and the FRET toolbox provides a large choice of luminescent materials, including dyes, lanthanide complexes, fluorescent proteins, quantum dots, and upconversion nanoparticles. 4,5 Noble metal nanoparticles can further extend the analytical distance range via nanosurface energy transfer (NSET),6,7 which is similar to FRET. Adding the broad choice of biological recognition molecules, including antibodies, artificial protein binders, aptamers, nucleic acids, or peptides to the versatility, sensitivity, and specificity of the world of FRETomics provides a boundless source for designing fluorescent probes for biosensing, bioimaging, and theranostics. 8-12 The presentation will explain time-resolved and time-gated FRET and the specific benefits for spectral and temporal luminescence multiplexing with different materials and instruments. Then, recent applications of multiplexed FRET biosensing, bioimaging, and theranostics with hybrid lanthanide-nanomaterials in solution, invitro, in-situ, and in-vivo will be discussed