Disease phenotyping is a key step towards an increasingly personalized approach to chronic obstructive pulmonary disease (COPD), leading to a more precise assessment, treatment and definition of disease outcomes. The search for biomarkers able to guide the identification of COPD phenotypes are of great importance for both researchers and clinicians. However, while several biomarkers of inflammation [e.g., peripheral blood eosinophils and fractional expired nitric oxide] have been identified and applied in asthma, none has been successfully linked to discrete clinical parameters of COPD such as exacerbations, natural progression, and treatment response or mortality risk. Recently, several studies have shown that blood eosinophils are a potential biomarker for patient subset stratification in COPD therapy. Here we reviewed the value of blood eosinophils in predicting the response of COPD patients to treatment.