  Solar magnetic fields are generated in the solar interior and pop up at the
solar surface to form active regions. As the magnetic field appears on the
surface, it forms various structures like small magnetic elements, pores, and
sunspots. The nature of these formation processes is largely unknown. In this
contribution we elaborate on the formation of sunspots and particularly on the
formation of penumbrae. We report on observations that we obtained at the
German VTT on July 4, 2009 on the formation of the spot in AR 11024. This data
set is accomplished with data from SOHO/MDI which offers an entire time
coverage. Moreover, the evolution of AR 11024 is compared with a particular
event of penumbra formation in AR 11124 around November 13, 2010, using
intensity images from SDO/HMI. We conclude that two processes contribute to the
increase of the magnetic flux of a sunspot: (1) merging pores, and (2) emerging
bipoles of which the spot polarity migrates towards and merges with the spot.
As the penumbra forms the area, magnetic flux, and maximum field strength in
the umbra stay constant or increase slightly, i.e. the formation of the
penumbra is associated with flux emergence and an flux increase of the
proto-spot. If two pores merge or if a pore merges with a proto-spot a light
bridge is created. This initial light bridge dissolves in the further
evolution.
