The following links lead to the 14 G-films that make up the Showa ("First Generation") Era series of G-films, as well as a brief description and episode guide of Godzilla's appearances on Toho's Zone Fighter, The Meteor Man TV series, which took place during the Showa Era, and the 'In Between Years of Godzilla' section, which describes the various G-film projects, both authorized and unauthorized, that were proposed during the nine year gap between the Showa Series (which ended abruptly with Terror of Mechagodzilla [1975]) and the Heisei Series (which began with Godzilla 1985 [1984]). The Showa Era series follows one consistent timeline (despite various incongruities along the way over its 20 year history), and the series never ended in a definitive manner, but simply ceased production following 1975 when Toho determined that the G-series of films' popularity and audience attendance had waned to the point where it no longer justified the ever-shrinking budgets previously alloted to keep the series going. For a more in-depth discussion of the lengthy uphill battle series producer/executive producer Tomiyuka Tanaka faced to eventually return the Atomic Titan to the big screen [after scrapping the Showa Series continuity for good, which he blamed for the series' eventual loss of popularity as a result of Godzilla's slow metamorphosis from a deadly serious destructive menace to humankind to a campy, kid-friendly heroic defender of the human race], see the section on The In-between Years Of Godzilla.
Please note that each of the films listed below feature the Japanese release date, and not the American release date, as these movies were usually released later (and sometimes significantly later) in America, rather than simultaneously with their release across the Pacific, a practice continued to this day.
GODZILLA SHOWA ERA FILM SERIES
Godzilla Raids Again (1955)
King Kong vs. Godzilla (1962)
Godzilla vs. Mothra (1964)
Ghidrah, the Three Headed Monster (1964)
Godzilla vs. Monster Zero (1965)
Godzilla vs. the Sea Monster (1966)
Son of Godzilla (1967)
Destroy All Monsters (1968)
Godzilla's Revenge (1969)
Godzilla vs. the Smog Monster (1971)
Godzilla vs. Gigan (1972)
Godzilla vs. Megalon (1973)
Godzilla on Zone Fighter, the Meteor Man TV series (1973)
Godzilla vs. Mechagodzilla (1974)
Terror of Mechagodzilla (1975)
The In-Between Years of Godzilla