Reynolds leads a research group focused on the astrophysics of black holes and related high-energy processes. Specific current interests include (i) the imprints of strong gravity on X-ray spectral and timing data and subsequent constraints on black hole spin; (ii) observational constraints and theoretical models for winds from AGN; (iii) the theory of black hole accretion, connecting the modern MHD-turbulence paradigm for accretion disks to observables; (iv) observational constraints on AGN feedback in massive galaxies and galaxy clusters; (v) theoretical models of AGN feedback and the relevant plasma physics of the intracluster medium, (vi) astrophysical probes of particle physics beyond the Standard Model (particularly constraints on axion-like particles), (vii) development of future X-ray observatories. Throughout his career, Reynolds has integrated students of all levels (undergraduate, masters, and PhD) as well as early career postdoctoral researchers into his research group. To date, he has mentored 13 PhD students through to graduation, with another 4 PhD students currently working with him in Cambridge. He has been the primary research advisor for 19 early career postdoctoral research associates and fellows.