Optical imaging technologies, such as optical coherence tomography (OCT), have the potential to acquire exquisitely high-resolution images of tissue and provide surgeons with a new generation of intra-operative guidance tools. However, their limited image penetration depth of only a few millimetres places most diseases beyond their reach. Our team has focused on the development of OCT needle probes: highly miniaturized imaging probes that are encased within a hypodermic needle, and that may be inserted deep into tissue. In this talk, I will describe our development of OCT needle probes, and give specific case studies of clinical applications. Recently, we have integrated our probes into brain biopsy needles to enable safer neurosurgery, and have performed our first experiments in humans. In addition, we have developed the first dual-modality needle probes, capable of simultaneously acquiring OCT and fluorescence images, and showed them to be sufficiently sensitive to detect signal from fluorescently-labelled anti-bodies targeted for specific cells types.