Optical coherence tomography angiography (OCT-A) is a new non-invasive technology for imaging of retinal and choroidal vasculature of the macular area with resolution comparable to histological sections. OCT-A does not require usage of intravenous dye, contrary to fluorescein angiography, the current gold standard for imaging of retinal vessels, and indocyanine-green angiography, which is important for imaging of choroidal vessels. With the advancements in optical coherence tomography (OCT) scanning speeds and creation of powerful algorithms for improvement of image quality in recent years, OCT-A imaging of macular vasculature, superficial, deep and avascular retinal complex, as well as choriocapillaris and deep choroid has become available in everyday clinical practice. This review covers aspects important for understanding choroidal and retinal blood supply, as well as the development, mechanisms and clinical application of OCT and OCT-A technology.