Over the last few years, great advances in our understanding in tumor neovascularization have emerged, with several new mechanisms of neovascularization being proposed. Solid tumors establish a vasculature through angiogenesis, vasculogenesis, vascular remodeling, co-option, and possibly also intussusception and vascular mimicry. Quantitative measurements of the tumor vasculature have generally measured the number of microvessels, highlighted using immunohistochemistry and antibodies to factor VIII-related antigen at high power over a defined field area. The generation of more sensitive and specific markers—in particular antibodies to CD34—together with the use of a Chalkley eyepiece graticule have improved the objectivity of the assessment of tumor vascularity. The protocol for this is discussed, with several variations such as vascular grade, microvessel density, and the alterations required for the assessment of vascularity in in situ breast disease. Also outlined are potential other measures of the angiogenic activity of breast tumors including the use of angiogenic factors and their receptors, endothelial cell proliferation, vessel maturation index, cell adhesion molecules, proteolytic enzymes, and the recently identified hypoxic markers.