In this project, Inductively Coupled Plasma (ICP) etching of natural and synthetic diamond using oxygen-based (Ar/0₂) and chlorine-based (Ar/Cl₂) plasmas was investigated. The effects of ICP platen and coil powers and gas pressures on the diamond etching were also studied. It was demonstrated that the diamond etch rate and etch selectivity using Ar/Cl₂ plasma etching, with high etch controllability (on the nanometre scale) and capabilities of removing the sub-surface damage and improving the surface smoothness, is only half of those by using Ar/0₂ plasma. Based on these studies, various diamond micro-optics including diamond microspherical positive and negative lenses, micro-cylindrical and micro-ring lenses, complex micro-lenses and optical gratings were designed and successfully fabricated. Structural and optical characterisations revealed the high optical quality and functionality of the fabricated diamond micro-optics. Applications of diamond micro-optics, such as micro-lensed micro-VECSEL photonic devices were also demonstrated. Utilising ICP Ar/Ch plasma etching and other processes, prototype diamond electronic devices such as diamond MISFETs and MOSFETs have been fabricated. To realize such diamond FET devices, ohmic contacts with low specific contact resistances, which can be achieved by applying aqua regia surface treatment and laser ablation techniques on the p-doped diamond, are imperative. However, it was found that the gate leakage currents of the diamond MISFET devices were quite large due to leakage through the diamond intrinsic layer under the gate. To overcome this problem, diamond MOSFET devices employing Si0₂ as gate insulation material were developed, which were able to sustain large gate biases with very low leakage currents. However, these diamond MOSFET devices could not be fully pinched-off which may be due to the high boron concentration and relatively thick delta layer, which leads to excessive charge in the channel of the device. By fabricating a recess gate diamond p-MOSFET, gate field control was much enhanced.