The UTLS Aerosol Measurement Package comprises three individual instruments for the measurement of aerosol number size distribution in the upper troposphere and lower stratosphere: a Nucleation Mode Aerosol Size Spectrometer (NMASS), an Ultra-High Sensitivity Aerosol Spectrometer (UHSAS), and a Portable Optical Particle Spectrometer (POPS). These instruments, along with a Passive, Near-Isokinetic Inlet for sampling atmospheric particles from a fast-moving aircraft, provide a measurement of the UT/LS particle size distribution from 4 to 3000 nm diameter. Aerosol microphysical measurements in the UT/LS are integral to understanding the chemical and radiative processes that control the Earth’s climate, and UTLS-AMP provides data for investigation of topics ranging from new particle formation to long range transport of dust and fine volcanic ash.