The basic photochemical processes in the upper atmospheres and ionospheresof the various bodiesin our solar system (planets, moons and comets)are similar. However, there are many different factors (e.g. gas composition, energy input, gravity) which control/change the relative importance of these controlling processes. The photo-chemistry of the inner planets is reasonably well understood at this time, thus there is good agreement betweenmodel calculations and most of the observationaldata base. The extremely limited informationthat we have available on the ionospheres of the outer planets leads to significant uncertainties about some of the controlling processes. Someimportantquestions(e.g. Is the charge exchangeprocess H+ + H2(v4) -. H2++ H important? Is watervapor influxfrom the rings important?)remainunansweredat this time. In cometary atmospheres the freshly evaporated parent molecules are rapidlyphotodissociated and photoionized, therefore most of the chemical kineticsof cometaryionospheresinvolvetheserapidlymovingand highly reactive ionsand radicals.