Cells endogenously express many different receptors that can activate the same second messenger, but with remarkably diverse physiological outcomes. This suggests a high degree of organisation and regulation of intracellular signalling, which is achieved by the spatiotemporal compartmentalisation of signals -the restriction of second messengers in space and time. The development of targeted Bioluminescence Resonance Energy Transfer (BRET) and Forster (F)RET-based biosensors has increased the resolution at which we can measure the spatial and temporal signalling of GPCRs. This technology has revealed that GPCRs can activate very defined signals in limited sub-cellular compartments. GPCRs do this by assembling focused "platforms" for specific signalling. These signalling platforms facilitate second messenger production, the organisation and scaffolding of effectors, and co-ordination of regulatory elements. This spatial and temporal control of signalling by GPCRs define the physiological outcomes of receptor activation. This presentation will focus on the use of targeted RET biosensors to understand the sub-cellular dynamics of GPCR activation, and how this is controlled by receptor trafficking.