Observatory Filter Anamorphic Optics Grating Spectrometer Herschel Telescope Entrance Optics – Calibration – Cold Lyot Stop – Sky Chopper Spectrometer Image Slicer MagnifierPhotometerOptics Dichroic Beamsplitter Photometer Blue Bolometer Array retliFleehW retliF Filter Wheel Red Photoconductor Array

The Photodetector Array Camera and Spectrometer (PACS) is one of the three science instruments on ESA’s far infrared and submillimetre observatory. It employs two Ge:Ga photoconductor arrays (stressed and unstressed) with 16 × 25 pixels, each, and two filled silicon bolometer arrays with 16 × 32 and 32 × 64 pixels, respectively, to perform integral-field spectroscopy and imaging photometry in the 60−210 μm wavelength regime. In photometry mode, it simultaneously images two bands, 60−85 μm or 85−125 μm and 125−210 μm, over a field of view of ∼1.75′ ×3.5′, with close to Nyquist beam sampling in each band. In spectroscopy mode, it images a field of 47′′ × 47′′, resolved into 5 × 5 pixels, with an instantaneous spectral coverage of ∼ 1500 km s−1 and a spectral resolution of ∼175 km s−1. We summarise the design of the instrument, describe observing modes, calibration, and data analysis methods, and present our current assessment of the in-orbit performance of the instrument based on the performance verification tests. PACS is fully operational, and the achieved performance is close to or better than the pre-launch predictions.