Vulvar intraepithelial neoplasia (VIN) is the currently accepted generic designation for the spectrum of vulvar lesions with the histologic features of squamous dysplasia and squamous cell carcinoma in situ. Although several classifications of VIN have been espoused in the past 20 years, VIN can be readily classified into two principal clinicopathologic types: classic (bowenoid) VIN and simplex (differentiated) VIN. This manuscript summarizes the historical development and current status of our knowledge about VIN. Information on the clinical and pathologic aspects are detailed and illustrated, as are considerations of differential diagnosis.