This thesis presents on the characterisation of numerous point defects in diamond grown by chemical vapour deposition (CVD). This has been facilitated primarily by photoluminescence (PL), in conjunction with techniques including uniaxial stress, charge transfer, irradiation, and annealing. Two defects commonly observed in as-grown CVD diamond; with zero phonon lines (ZPLs) at 389 and 468nm are investigated. Uniaxial stress measurements suggest possible symmetries for the 389nm centre of C2v or D2d, with the 389nm ZPL being the result of an A ←→ B transition. The temperature dependence of PL from the 468nm centre is measured, and unambiguously shows that a feature at 464nm is a second ZPL of the 468nm centre. UV-Vis absorption in conjunction with a charge transfer protocol suggests that the 468nm centre is negatively charged, and an irradiation study shows that this defect readily donates electrons to neutral lattice vacancies (V0). An irradiation and annealing study is made on type IIa CVD diamond containing in the range of 1 – 5 ppb of nitrogen, with irradiation facilitated by a transmission electron microscope (TEM). The production rate of vacancies during irradiation with 200 keV electrons is shown to be approximately 0.005 (vacancies/ electron)/cm. TEM irradiation is demonstrated to be a controllable method for the formation of defects; a GR1 PL linewidth of 0.77meV is measured, and negatively charged nitrogen vacancies (NV-) are formed with T2 times approaching 13C limited values. The properties of a centre with a ZPL at 733nm are shown to be consistent with an assignment to the divacancy defect. A TEM irradiation and annealing study is carried out on CVD diamond co-doped with silicon and nitrogen. Further evidence is shown for the existence of the doubly negatively charged silicon vacancy (SiV2-), in the form of charge transfer with V0. A new mechanism for cathodoluminescence emission from SiV- is proposed involving the capture of a hole by SiV2-. A significant number of unidentified ZPLs are observed. Among them are defects emitting at 486 and 520nm, which are tentatively assigned to complexes involving silicon and carbon interstitials.