Lung ventilation is a mechanical process in which the respiratory muscles are acting in concert to remove air in and out of the lungs. Any alteration in the performance of the respiratory muscle may reduce the effectiveness of ventilation. Thus, early diagnosis of their weakness is vital for treatment and rehabilitation. Different techniques, which are based on different measurement protocols, can be utilized for evaluation of respiratory muscle strength. Respiratory muscle strength can be assessed using pressure measurement either from the mouth or from the nostril during quasi-static breathing. However, it estimates only global performance of respiratory muscles. Techniques that are based on electromyography measurements during muscle contraction (EMG) enable the differentiation between the different respiratory muscles. Along with the above clinical and physiological techniques for assessment of respiratory muscle strength and endurance, mechanical and mathematical models of the chest wall were developed in the last few decades for analysis of chest wall movements and the contribution of its components to respiration. In this review, the different methods and the models utilized for evaluation of respiratory muscles function will be discussed.