Ductal carcinoma in situ (DCIS) of the breast is a non-obligatory precursor to invasive breast carcinoma, with a variable natural history and biological potential for progression to invasive disease. Over the past 30 years, clinical trials have applied the therapeutic principles used for invasive carcinoma to treat DCIS (surgery, with or without breast radiotherapy, and post-operative endocrine therapy), with excellent survival outcomes, and in-breast recurrence rates that range from 0.5 to 1% annually. However, half of such recurrences are again in-situ lesions, and intensive therapy is likely not necessary for all patients. Current clinical research is focused on a better characterization of the potential of individual lesions to progress to invasive disease, and to identify women who would do well with lesser treatment. Three ongoing trials in the United States and Europe randomize women to active surveillance (with or without endocrine therapy) versus usual treatment with surgery and radiotherapy. The use of pre-operative endocrine therapy has been evaluated in a recently completed trial of letrozole use in postmenopausal women with DCIS; and in on-going trials of tamoxifen, used either orally, or as a 4-hydroxytamoxifen gel formulation for application to the breast skin. This review summaries the major past and current clinical trials of DCIS, and the likely trajectories of DCIS management in the near future.