A new sampler for the collection, sizing, and enumeration of viable airborne particles is described. The Andersen sampler consists of six stages with 400 holes each, designed to collect particles based on their aerodynamic dimensions. Air is drawn through the device at a rate of 1 cubic foot per minute (cfm), and particles are collected on different stages depending on their size. The sampler is pressure-sealed and made of aluminum alloy with stainless steel fittings. It is lightweight, efficient, and capable of collecting a wide range of particle sizes, including those as small as 1 micron. The sampler is designed to minimize wall loss and slippage, ensuring that viable particles are collected without being lost or passing through the device. It is highly sensitive and can detect even small numbers of viable particles. The sampler uses agar plates to collect particles, which are then incubated and counted. The number of positive holes on the plates is used to estimate the number of viable particles, with a conversion table providing a more accurate count. The Andersen sampler has been tested with various materials, including bacteria, wax, and egg slurry, and has shown excellent performance in collecting and sizing particles. It is particularly effective in collecting bacterial aerosols and has been used in studies of bacterial decay and transmission. The sampler is also useful for studying the effects of suspending media on particle size and for collecting radioactive particles for Geiger counter readings. The Andersen sampler is more efficient than traditional sampling devices, such as the all-glass impinger, as it requires less labor and time, and provides more accurate and meaningful results. It is suitable for assessing health hazards in particulate air pollution and for detecting and identifying pathogenic organisms. The sampler is also useful for collecting and analyzing aerosolized bacterial phage and other biological particles. The Andersen sampler is a valuable tool for environmental and public health studies.A new sampler for the collection, sizing, and enumeration of viable airborne particles is described. The Andersen sampler consists of six stages with 400 holes each, designed to collect particles based on their aerodynamic dimensions. Air is drawn through the device at a rate of 1 cubic foot per minute (cfm), and particles are collected on different stages depending on their size. The sampler is pressure-sealed and made of aluminum alloy with stainless steel fittings. It is lightweight, efficient, and capable of collecting a wide range of particle sizes, including those as small as 1 micron. The sampler is designed to minimize wall loss and slippage, ensuring that viable particles are collected without being lost or passing through the device. It is highly sensitive and can detect even small numbers of viable particles. The sampler uses agar plates to collect particles, which are then incubated and counted. The number of positive holes on the plates is used to estimate the number of viable particles, with a conversion table providing a more accurate count. The Andersen sampler has been tested with various materials, including bacteria, wax, and egg slurry, and has shown excellent performance in collecting and sizing particles. It is particularly effective in collecting bacterial aerosols and has been used in studies of bacterial decay and transmission. The sampler is also useful for studying the effects of suspending media on particle size and for collecting radioactive particles for Geiger counter readings. The Andersen sampler is more efficient than traditional sampling devices, such as the all-glass impinger, as it requires less labor and time, and provides more accurate and meaningful results. It is suitable for assessing health hazards in particulate air pollution and for detecting and identifying pathogenic organisms. The sampler is also useful for collecting and analyzing aerosolized bacterial phage and other biological particles. The Andersen sampler is a valuable tool for environmental and public health studies.