Metal halide perovskites (MHPs) are a diverse family of materials that have had a colossal impact in photovoltaic and other emerging optoelectronic devices where they outperform incumbent materials and continue to deliver delivering outstanding performance. The intense volume of active research being carried out on MHPs is driven by their unique properties including their tuneable bandgap, large absorption coefficients, large charge carrier diffusion lengths and charge carrier mobilities combined with their relative ease of synthesis. Unfortunately, the synthetic methods that have been developed for depositing MHPs rely on the use of solvents harmful to human  health and the environment, furthermore the synthetic protocols have an intrinsic requirement for multi-component solvent systems and a fundamental need for thermal treatment during processing to ensure the desired phases are prepared. Here we give an overview of a number of novel synthetic strategies we have been developing in our  laboratory aimed at identifying routes for MHPs–thin films, nanocrystals, single crystals – prepared using green solvents and without the need for extensive thermal processing. We will elaborate a novel solvent system and synthetic method for the preparation of size and compositionally controlled MHP nanocrystals. Remarkably our synthesis is carried out using a water-based solvent and is achieved in ambient air and at room temperature. We show the synthesis of size controlled CsPbBr₃ nanocrystals with a photoluminescence quantum yield (PLQY) > 60 % and through anion exchange demonstrate the formation of a range of CsPbX₃ (X = I, Br, Cl) nanocrystals that cover an emission range of 450 to 660 nm. Our novel, green solvent offers a clean, scalable and low-cost route for size and compositional control of MHP nanocrystals.