Diamond is an exceptional material - hard, stiff, transparent, which makes it ideal for the fabrication of optical and mechanical systems that take advantage of these properties. Diamond is not only "better", but it offers the possibility of integrating bright colour centres. These optically active defects can be exploited for a variety of applications, including the study of fundamental science, magnetometry, biosensing and new types of lasers. Despite the attractive properties of diamond for optics, no standard platform exists to create photonic circuits and devices. This thesis shows the realisation of a diamond-on-insulator photonics platform, that aims to combine the versatility of the silicon-on-insulator photonics with the capability of performing diamond science in single crystal guided-wave devices. The diamond-on-insulator substrate is achieved via ion implantation-based cut of a single crystal membrane and bonding of the membrane to an insulator layer. This approach provides a monolithic fabrication process that scales to commercial exploitation, bringing convenient access to the study of diamond light-matter interactions without requiring custom substrate fabrication. Furthermore, the possibility of releasing the diamond devices adds access to freestanding structures, opening the way to diamond micro-opto-electro-mechanical systems and optomechanics. Diamond also makes an excellent microoptics substrate, due to its high laser damage threshold, transparency and high refractive index, which is an attractive combination for high-power, compact optical systems operating in the UV, visible and near-infrared. Different diamond etching techniques are developed and investigated in this thesis, that enable the realisation of unique features. These techniques are employed to create diamond diffractive microoptical components, which are then characterised, showing high-quality surfaces that closely match the designed features, indicating reliable fabrication and resulting in excellent optical performance. These devices have applications in high power beamsplitters, beam shapers and compact spectrometers.