Spacers and valved holding chambers (VHCs) are widely used in conjunction with inhalation aerosols [commonly known as pressurized metered-dose inhalers (MDIs)]. When used correctly, VHCs assist with the administration of inhalation aerosols to patients who have poor coordination of MDI actuation and inhalation, and VHCs reduce oro-pharyngeal deposition of the drug. Patients using these spacers/VHCs in general breathe tidally when inhaling their medication, regardless of any delay, and this is particularly true for young and elderly users. Also, spacers and VHCs often come with a facemask instead of the mouthpiece normally supplied for inhalation aerosols. These add-on devices (spacers/VHCs) interface with the actuator/mouthpiece of the MDI and provide additional volume for the aerosol plume to develop. In this chapter, these aspects are addressed by providing patient-use appropriate scenarios that have been evaluated extensively.