LiNbO3 and LiTaO3 are commonly used ferroelectric crystal materials. Since the first reports of successful single domain crystal growth in 1965, these materials have found increasing use in optoelectronics, laser systems, Q- switching and frequency conversion, holographic data storage, surface acoustic wave devices, integrated optics and modulator use, and most recently, microwave telecommunications. In single domain format these ferroelectrics are photorefractive, pyroelectric and piezoelectric, and possess usefully large nonlinear optical and electro-optical coefficients. If domain engineering or micron/nano-scale bulk or surface modification is performed however, greater functionality is introduced, leading to additional uses such as phase-matched frequency conversion, grating and photonic structures, and the recently proposed use in MEMS and MOEMS devices. We discuss here a range of techniques for domain engineering and domain selective etching, as well as the use of light in poling and etching modification, and illustrate this potential with several devices that we have constructed by these routes.