Asthma and chronic obstructive pulmonary disease (COPD) arethe two most prevalent obstructive diseases of the lung. Althoughasthma and COPD differ in many ways some properties of eachdisease co-exist in some patients, particularly in patients withadvanced age which recently brought up the term; Asthma-COPDOverlap Syndrome (ACOS). In addition to the fact that clinicaltrials deliberately exclude the patients in this group, the diagnosticcriteria of ACOS are not well established. Both of these factorscontribute to paucity of evidence based clinical information aboutACOS. In this article my aim is to provide brief information aboutthe history, description, clinical properties and treatment of thisdisease.