Abstract Context.—Interpretation of papillary lesions of the breast remains a challenging task because of the wide morphologic spectrum encountered in the benign, atypical, and malignant subtypes. Data on clinical significance and outcome of papillary lesions, with superimposed atypia or areas similar to ductal carcinoma in situ partially replacing the benign elements, are sparse. Furthermore, complete excision of even a fully developed papillary carcinoma confined to a dilated or cystic duct is associated with an excellent prognosis, whereas a complex papilloma extending into multiple branches of a duct may ultimately recur as a carcinoma because of incomplete excision of microscopic foci. This makes an outcome-based classification difficult. Objective.—An arbitrary yet practical approach to classification is outlined, with discussion of methods to circumvent the various diagnostic difficulties. The limitations in precise diagnosis of papillary lesions in aspirates are addressed, and the implications of finding papillary lesions in core biopsies are discussed. Although the focus is on intraductal lesions, associated invasive carcinomas and invasive micropapillary carcinoma are also presented. Data Sources.—The literature on papillary lesions and invasive micropapillary carcinoma is reviewed. Conclusions.—It would be prudent to completely excise any papillary lesion that has not been entirely removed by the initial core biopsy. The optimal management of localized papillary lesions is complete excision with a small rim of uninvolved breast tissue without any prior needle instrumentation if and when the papillary nature can be determined by imaging. Thus managed, most of these lesions behave indolently, and outcome is usually excellent.