THE OBLIQUITY (AXIS TILT) OF A PLANET AND ITS VARIATION STRONGLY AFFECT CLIMATE AND BY EXTENSION A PLANET'S POTENTIAL FOR HABITABILITY. OBLIQUITY CAN VARY A SMALL AMOUNT LIKE THE EARTH'S IN THE PRESENCE OF OUR MOON. OR IT CAN VARY WILDLY LIKE MARS' WHICH TAKES VALUES BETWEEN 0 AND 60 DEGREES OVER 100 000-YEAR TIMESCALES. EACH OF THOSE VARIATION REGIMES ASSUMES THE PRESENT-DAY PARAMETERS OF EARTH AND MARS THOUGH WHILE IN REALITY BOTH ROTATION RATE AND OBLIQUITY ITSELF ARE AFFECTED BY TIDAL INTERACTION WITH THE SUN. WE WILL INVESTIGATE LONG-TERM CHAOTIC OBLIQUITY VARIATIONS AND THEIR EVOLUTION FOR TERRESTRIAL PLANETS OVER BILLION-YEAR TIMESCALES BY UNITING NUMERICAL OBLIQUITY TRACKING WITH TIDAL INFLUENCES. WHILE THE OBLIQUITY OF A PLANET IN A SINGLE-PLANET SYSTEM CAN BE TREATED ANALYTICALLY A MORE COMPLETE TREATMENT REQUIRES A NUMERICAL APPROACH. WE WILL EXPLORE THE CLIMATE VARIABILITY RESULTING FROM OBLIQUITY OVER THE LIFETIME OF THE SUN FOR EARLY VENUS MOONLESS EARTH MARS AND HYPOTHETICAL SYSTEMS AROUND M-DWARF STARS. WE EXPECT FOR OUR RESULTS TO BEAR ON NOT JUST THE INSTANTANEOUS HABITABILITY BUT ALSO THE LONG-TERM HABITABILITY OF BOTH OUR SOLAR SYSTEM PLANETS AND BY EXTENSION EXOPLANETS AS WELL. THIS PROPOSAL IS RELEVANT TO THE HABITABLE WORLDS PROGRAM GOAL TO "IDENTIFY THE CHARACTERISTICS AND THE DISTRIBUTION OF POTENTIALLY HABITABLE ENVIRONMENTS IN THE SOLAR SYSTEM AND BEYOND" BECAUSE IT WILL HELP TO EVALUATE THE ROTATIONAL AND ORBITAL PARAMETERS THAT INFLUENCE LONG-TERM HABITABLE TERRESTRIAL ENVIRONMENTS AS AFFECTED BY TIDES.