Book excerpt: Both the Food and Drug Administration (FDA) and the National Institute for Occupational Safety and Health (NIOSH) have responsibilities for evaluating and regulating respiratory protective devices ("respirators") for health care workers. Respirators protect the user from respiratory hazards by either removing contaminants from the air (air-purifying respirators) or by supplying clean air from another source (air-supplying respirators). Respirators that are used in workplaces in the United States must be approved by NIOSH and meet standards and test results specified by regulation. Respirators used by health care workers are air-purifying respirators that generally fall into three types: (1) disposable particulate filtering facepiece respirators (also termed N95s); (2) elastomeric respirators, also known as reusable respirators because they use a replaceable filter; or (3) powered air-purifying air respirators. To provide input to NIOSH and FDA and to discuss potential next steps to integrate the two agencies' processes to certify and approve N95 respirators for use in health care settings, a workshop was held by the National Academies of Sciences, Engineering, and Medicine in August 2016. The workshop was focused on exploring the strengths and limitations of several current test methods for N95 respirators as well as identifying ongoing research and research needs. This publication summarizes the presentations and discussions from the workshop.