This is a Phase 3, randomized, double-blind, placebo-controlled, parallel-group, multicenter, efficacy and safety trial of 12 weeks of treatment with nebulized SUN-101 using an Investigational eFlow® Closed System (CS) nebulizer in approximately 645 subjects with chronic obstructive pulmonary disease (COPD) according to the Global Initiative for Chronic Obstructive Lung Disease (GOLD 2014) guidelines.