The International Society for the Study of Lung Cancer, the American Thoracic Society, and the European Respiratory Society (IASLC, ATS, ERS) jointly published new international multidisciplinary classification criteria for adenocarcinoma of the lung in the Journal of Thoracic Oncology (J Thorac Oncol) in 2011. For the first time, separate classification methods were proposed for surgical resection specimens, small biopsies and cytology; the concepts were updated and changed significantly, such as the names of bronchoalveolar carcinoma (BAC) and mixed adenocarcinoma in situ (AIS) and minimally invasive adenocarcinoma (MIA) were no longer used. The names of adenocarcinoma in situ (AIS) and minimally invasive adenocarcinoma (MIA) were replaced by the names of adenocarcinoma in situ (AIS) and minimally invasive adenocarcinoma (MIA). AIS is defined as a small adenocarcinoma (≤3 cm) with limited, squamous growth of tumor cells along the alveolar wall without interstitial, vascular, or pleural infiltration, and MIA is defined as a small adenocarcinoma (≤3 cm) with isolated, predominantly squamous growth and infiltrative foci ≤0.5 cm. AIS and MIA usually present as non-mucinous or very rare mucinous subtypes, and patients in these two categories have a disease-specific survival rate of 100% or nearly 100%, respectively, if they undergo radical surgery. Second, invasive adenocarcinoma can be divided into subtypes with predominantly squamous, follicular, papillary, and solid growth patterns, and a new subtype of “micropapillary growth pattern” is recommended because of its association with poor prognosis. The former WHO classification of clear cell adenocarcinoma and indolent cell adenocarcinoma were included in the solid-based subtypes. Secondly, the variants of invasive adenocarcinoma include invasive mucinous adenocarcinoma (formerly mucinous BAC), colloid adenocarcinoma, fetal adenocarcinoma, and intestinal adenocarcinoma. The intestinal type, on the other hand, is a newly proposed subtype, which should be morphologically differentiated from adenocarcinoma of gastrointestinal origin. Finally, a comprehensive and detailed histological diagnostic model is advocated for invasive adenocarcinoma, instead of generalizing it to a mixed subtype. An example of diagnostic pattern: lung adenocarcinoma with a predominantly solid growth pattern, 10% with an alveolar-like growth pattern and 5% with a papillary growth pattern; in the previous WHO classification, a tumor component (a particular growth pattern) was considered as a constituent only when it reached 10%, whereas the new classification recommends that it should be described in the diagnosis as soon as it reaches 5%.