The ultra-low surface brightness universe remains the last niche to be explored in observational parameter space, due to the strong biases that exist in the current instrumentation, both ground- and space-based.

Yet observing the universe at levels which are a tiny fraction brighter than the sky background reveals a wealth of astrophysical objects whose properties appear to be entirely different from those at brighter surface brightness levels, from huge extended galactic discs to the filaments of the cosmic web, through the revision of the abundance of dwarf galaxies and the role of intracluster light and the fluctuations of the yet-undetected UV-optical cosmological background radiation.

The main aims of our ISSI International Team will be:

(i) to review critically the current observations;

(ii) to compare them to theoretical models; and

(iii) to propose novel ground- and space-based instrumentation pathways to further explore this realm, both in the optical and in the UV range.