[en] Free-Electron Lasers (FELs) operated in the self-amplified spontaneous emission (SASE) mode start from shot-noise. The chaotic behaviour of this statistical process entails limited longitudinal coherence and spectral shot-to-shot stability of the emitted photon pulse. These drawbacks can be overcome by seeding the FEL process with an external light field. The linear accelerator at the FLASH user facility drives two undulator beamlines, FLASH1 and FLASH2. At FLASH1, the seeding experiment comprises two electro-magnetic undulators, three chicanes, and a variable-gap undulator system. Thanks to this variable infrastructure, the FLASH1 seeding beamline is an ideal test bed to study different seeding schemes and to learn from experiments for the design of FLASH2 seeding. In this contribution we report on current activities at FLASH1 and possible seeding options for the second FEL beamline FLASH2.