  Magnetic fields emerging from the Sun's interior carry information about
physical processes of magnetic field generation and transport in the convection
zone. Soon after appearance on the solar surface the magnetic flux gets
concentrated in sunspot regions and causes numerous active phenomena on the
Sun. This paper discusses some properties of the emerging magnetic flux
observed on the solar surface and in the interior. A statistical analysis of
variations of the tilt angle of bipolar magnetic regions during the emergence
shows that the systematic tilt with respect to the equator (the Joy's law) is
most likely established below the surface. However, no evidence of the
dependence of the tilt angle on the amount of emerging magnetic flux, predicted
by the rising magnetic flux rope theories, is found. Analysis of surface plasma
flows in a large emerging active region reveals strong localized upflows and
downflows at the initial phase of emergence but finds no evidence for
large-scale flows indicating future appearance a large-scale magnetic
structure. Local helioseismology provides important tools for mapping
perturbations of the wave speed and mass flows below the surface. Initial
results from SOHO/MDI and GONG reveal strong diverging flows during the flux
emergence, and also localized converging flows around stable sunspots. The wave
speed images obtained during the process of formation of a large active region,
NOAA 10488, indicate that the magnetic flux gets concentrated in strong field
structures just below the surface. Further studies of magnetic flux emergence
require systematic helioseismic observations from the ground and space, and
realistic MHD simulations of the subsurface dynamics.
