Interstitial lung diseases form one of the most complex and ill-understood areas in pulmonary medicine. The approach to interstitial lung disease therefore, in most instances, is necessarily multi-disciplinary. From the imaging perspective, pattern identification constitutes an important aid to diagnosis. This chapter characterises the patterns of interstitial involvement and associated abnormalities as they appear on HRCT scans, which taken in context, help in clarifying the etiological possibilities.