The release of the MUSE Hubble Ultra-Deep Field survey (Programmes 094.A-0289(B), 095.A-0010(A), 096.A-0045(A), 096.A-0045(B) and 1101.A-0127, PI R. Bacon) includes the deepest spectroscopic survey ever performed. The MUSE mosaic data cubes, with their 3D content, amazing depth, wide spectral range, and excellent spatial and medium spectral resolution, are rich in information. The 3σ point-source flux limit of an unresolved emission line reaches 3.1×10-19 and 6.3×10-20 erg s-1 cm-2 at 10- and 141-hour depths, respectively. The redshifts of 2221 sources have securely been identified and measured. With the exception of eight stars, the collected sample consists of 25 nearby galaxies (z < 0.25), 677 [O ii] emitters (z = 0.25 - 1.5), 201 galaxies in the MUSE redshift desert range (z = 1.5 - 2.8) and 1308 Lyα emitters (z = 2.8 - 6.7). This represents an order of magnitude more than the collection of all spectroscopic redshifts obtained before MUSE in the Hubble ultra-deep field area (i.e., 2221 versus 292). At high redshift (z > 3), the difference is even more striking, with a factor of 65 increase (1308 versus 20).