High-gain free-electron lasers (FELs) are driven by bright electron bunches that allow the generation of short FEL pulses of high brightness, tunable wavelength and high peak power. Short-wavelength FEL radiation is commonly provided by the self-amplified spontaneous emission (SASE) mechanism which leads to, due to its stochastic nature, FEL pulses of poor temporal coherence. To overcome this, external seeding techniques are used to generate fully coherent and stable radiation in the soft x-ray regime. The manipulation of electron beams with an external seed laser is the key to transforming FELs into a fully coherent light source, opening the door to fascinating experiments in FELs. Let us discuss external seeding methods and how we can extend in the future the highest repetition rate and shortest wavelength of externally seeded radiation to allow even more experiments to benefit from the unique properties of the radiation.