We propose to address the following topics (a non-exhaustive list):
- Overview: ULXs in X-rays and other wavelengths
- Accretion disk theory and the launching of jets or winds
- Which ULXs have collimated jets?
- Is SS 433 a ULX?
- Jets/winds and their interaction with the ISM: observations
- Jets/winds and their interaction with the ISM: theory
- Radiative and mechanical feedback
- Ultra-soft ULXs
- Transient ULXs
- Optical/UV/IR counterparts: disks and donor stars
- ULX populations: binary evolution, type of donor stars (main sequence or evolved?), duty cycles and timescales, clues from stellar populations and properties of the local ISM
- Influence of metallicity on ULX populations
- Radio-loud and radio-quiet ULXs (compact and FRII-like extended emission; synchrotron bubbles)
- Hyperluminous sources: a separate class of super-Eddington accretors, or true IMBHs?
- Similarities and differences between super-critical accretion onto stellar-mass BHs and neutron stars
- Latest XMM-Newton, Chandra, Swift and NuSTARS results
- Future missions (eg Athena)
