A population of isolated intergalactic HI clouds has yet to be recognized in the intergalactic medium. On-going high sensitivity studies of loose groups of galaxies, however, show that tidal debris in the form of HI streams is commonly found in such aggregates.

Recent observations of the Magellanic Stream can be used to set limits on a possible hot halo surrounding the Galaxy. The observations are described in detail elsewhere (Mirabel, Cohen & Davies, submitted to Mon. Not. R. astr. Soc.). Briefly, the neutral hydrogen in the northern end of the Magellanic Stream is concentrated in narrow filaments which contain small elongated clouds of typical size 0°.4 × 0°.6. These clouds have a large velocity halfpower width (25 km s−1 and are gravitationally unstable, unless there is a massive low luminosity stellar component. If we consider only the observed gas the expansion age of a typical cloud is 6 × 105 D years, where D is the distance in kpc from the Sun, and this falls at least a factor of ten short of the age of the Stream predicted by current models. This strongly suggests that some containment mechanism is operating.

Tidal interaction models for the origin of the Magellanic Stream have been fairly successful in reproducing the radial velocities of the Stream (Lin and Lynden-Bell 1977, Davies and Wright 1977). However, no investigator has yet attained a self consistent treatment in which (1) the LMC and SMC are bound for at least 5×109 yr, (2) the passing Magellanic Clouds warp the galactic plane, and (3) the Stream velocities are reproduced (Fujimoto and Sofue 1977). Also, Mathewson, Schwarz, and Murray (1977) argue that their 21 cm observations are evidence against the tidal model. To avoid these problems, they suggest that the Magellanic Clouds pass through a hot coronal gas and produce vortices in their wake which radiatively cool to form the HI clouds comprising the Stream.

Galaxies are like people. When you get to know one well it always turns out to be peculiar in some way or other. In many cases such peculiarities appear to be inherent whereas in others they seem to result from the environment in which a galaxy has evolved. Very few galaxies live in total isolation; most are members of cluster families. The purpose of the the present paper is to introduce the known members of the Local Group to you in the hope that a closer acquaintance with our closest relatives in space will ultimately lead to a deeper understanding of the structure and evolution of our own Milky Way system.

APOLOGIA: The edifice we call science is built of bricks contributed by many, many workers, laid according to a design too large to be comprehended by any one reviewer. My apologies, therefore, to all those whose bricks I have, through ignorance, prejudice, or lack of space, put in the wrong place, attributed to someone else, or ignored completely. Names cited below are generally those of the speakers who mentioned particular points. Proper references to who did what can thus be found in their papers and discussion remarks.

As mentioned already in Morton Roberts' fine introduction, two features were striking in this Symposium's programme: the broad spectral range of observational data, and the strong emphasis on comparisons with external galaxies. I shall return to the latter item towards the end of my summary. Let us first review the spectral panorama, then scrutinize what it has taught us about our Galaxy.

Many interesting new results from studies of external galaxies as well as of the Milky Way Galaxy have been presented at this meeting. I shall confine my remarks to but a few observations which appear to be crucial in deriving an acceptable picture of the large scale structure in the Galaxy.