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(Abridged) We present an overview of the sample of high-mass star and clusterforming regions observed as part of the Earliest Phases of Star Formation(EPoS) Herschel Guaranteed Time Key Program. A sample of 45 infrared-darkclouds (IRDCs) were mapped at PACS 70, 100, and 160 micron and SPIRE 250, 350,and 500 micron. In this paper, we characterize a population of cores whichappear in the PACS bands and place them into context with their host cloud andinvestigate their evolutionary stage. We construct spectral energydistributions (SEDs) of 496 cores which appear in all PACS bands, 34% of whichlack counterparts at 24 micron. From single-temperature modified blackbody fitsof the SEDs, we derive the temperature, luminosity, and mass of each core.These properties predominantly reflect the conditions in the cold, outerregions. Taking into account optical depth effects and performing simpleradiative transfer models, we explore the origin of emission at PACSwavelengths. The core population has a median temperature of 20K and has massesand luminosities that span four to five orders of magnitude. Cores with acounterpart at 24 micron are warmer and bluer on average than cores without a24 micron counterpart. We conclude that cores bright at 24 micron are onaverage more advanced in their evolution, where a central protostar(s) haveheated the outer bulk of the core, than 24 micron-dark cores. The 24 micronemission itself can arise in instances where our line of sight aligns with anexposed part of the warm inner core. About 10% of the total cloud mass is foundin a given cloud's core population. We uncover over 300 further candidate coreswhich are dark until 100 micron. These are candidate starless objects, andfurther observations will help us determine the nature of these very coldcores.

The Earliest Phases of Star Formation (EPoS): A Herschel Key Program - The precursors to high-mass stars and clusters