Potassium niobate (KNbO3) has great potential as a crystal for sum-frequency generation in the blue end of the spectrum, possessing, as it does, high nonlinear coefficients and high birefringence. However, concerns about wide-spread applications of the crystal in solid-state blue lasers persist; principally because of uncertainties surrounding the mechanical and thermal stability of the material. These instabilities result largely from the readiness with which ferroelectric domains can be formed within the crystal (at room temperature KNbO3 possesses an orthorhombic distortion of the parent perovskite crystal structure) by application of mechanical or thermal stress. In addition, fabrication of the as-grown crystal for device application requires removal of ferroelectric domains which result from cooling from the melt temperature, where the crystal is in the paraelectric cubic phase, through a tetragonal phase to the orthorhombic form. As part of a systematic investigation of the properties of KNbO3, we have characterized the nature of domain formation in as-grown crystals and have studied conditions under which single domain crystals are obtained by application of electric fields, using predominantly optical techniques. The electrical properties of the crystals are highly complex and appear to depend on a number of factors. We relate the extent of domain formation to crystal purity, size, and seed orientation.