Nanoscale domain engineering in ferroelectric crystals is demonstrated down to a lateral domain size of 25 nm in diameter using scanning force microscopy (SFM). The various modes of SFM are used to measure both the internal polarization field and external stray field arising from bound surface charges in ferroelectric domains. From these measurements the effective three-dimensional arrangement of ferroelectric domains is reconstructed. Domain switching is initiated applying strong electric fields between the tip and counter electrode. The size of freshly nucleated domains is found to depend dramatically on the switching conditions, i.e. the applied electric field strength and switching time. Domains of less than 100 nm in diameter result for an electric field E_exp>50 kV cm^-1 applied for an ultra-short time period τ_exp<30 μs. Also, the coercive field of nanoscale ferroelectric domains in BaTiO₃ single crystals is found to measure 1.4 kV cm^-1, much more than the bulk value. Analysis of the transient response during domain switching shows that domain nucleation proceeds within less than 100 μs. With these tools we are able to record nanoscale hysteresis loops monitoring both the successful domain reversal and a well established material contrast between different ferroelectric structures with a resolution of better than 0.1%.