HI Astronomy HI is the simplest but most abundant atom is space. Using todays radio astronomical technology, it is an easy task to measure the HI line emission. The sensitivity of the world's largest radio telescopes allow to detect the neutral species down to volume densities where the dominant gas fraction is already ionized. HI is of scientific key-importance for our understanding of galaxy formation, evolution and merging history, because even at large radial distances from the stellar body we can study in great detail the density, temperature and velocity structure of the neutral gas.

Single Dish Astronomy HI covers the whole sky! The Lockman area and the Chandra deep-field south area denote minimum column density regions where warm neutral medium reaches local minimum column densities, these are the windows to high-energy astrophysics sky. Despite the fact that neutral hydrogen itself has not the largest photo-electric cross section it is the tracer for the spacial distribution of heavier species, in particular for helium. HI full-sky single dish surveys are accordingly of high importance to quantify the amount of matter distributed along the line of sight. Towards high galactic latitudes the HI column density value itself is a measure for this quantity, within the Galactic plane, the radial velocity information allows to disentangle the HI line emission of different portions of the Galactic disk. Sophisticated modelling is necessary to disclose the complex structure of cold and warm gas but also offers the unique possibility to disclose the distribution of gravitational matter far beyond the stellar disk.

Radio Interferometry within the coming decade radio interferometers will survey at an unequaled angular resolution the whole sky. The prime scientific aim is to study the HI distribution at high red-shifts. Because of their construction radio interferometers blind for the radiation of very extended structures. Combining both, single dish and radio interferometer data, allow to disclose the whole structure of external galaxies even far away from the stellar body. APERTIF (The Netherlands) and ASKAP (Australia) will use focal plane arrays (FPAs) to observe the whole sky within a period of a few years. The combination of single dish and FPA interferometric data is a new task, which we like to establish as a member of an international consortium.

Effelsberg Bonn HI Survey (EBHIS) EBHIS is the first all-sky survey which aims to perform a blind survey of the Milky Way HI distribution and the local volume in parallel. Present day spectrometer allow to resolve the cold neutral medium lines and to measure the HI radiation of a Milky Way galaxy at a red-shift of 0.07 within a single dump. Making use of this ability we optimized EBHIS to cover the full northern sky at an unique signal-to-noise ratio for the Milky Way Galaxy and towards the Sloan-Digital-Sky Survey (SDSS) area with a signal-to-noise ratio that we can detect the HI emission of a $10^7\,{\rm M_\odot}$ galaxy at the distance of the Virgo cluster. While on cosmological scales the Universe appears isotropic and homogeneous, we know that the local volume towards the northern hemisphere offers a unique view towards the closest larger galaxy clusters, our large and massive local group spiral galaxies and a large variety of high-velocity cloud complexes which show-up with unique signatures of an on-going interaction with the Milky Way Galaxy.