Ubi bene, ibi patria.
Where one feels good, there is one's country.

Ubi dubium, ibi libertas.
Where there is doubt, there is freedom. (When in doubt, assume innocence).

Ubi fumus, ibi ignis.
Where there's smoke, there's fire.

Ubi maior, minor cessat..
When the older speaks, the younger should cease speaking.

Ubi mel ibi apes.
Where there's honey, there are bees.

Ubi tu Gaius, ibi ego Gaia.
Where you are, Gaius, there I, Gaia, will be. (Roman nuptial formula).

Ulula cum lupis, cum quibus esse cupis.
Who keeps company with wolves, will learn to howl.

Una hirundo non facit ver.
One swallow doesn't make spring.

Usus magister est optimus.
Practice makes perfect.

Ut desint vires, tamen est laudanda voluntas.
Even if the powers are missing, the will deserves praise. (Ovid)

Ut sementem feceris, ita metes.
You'll reap what you sow. (Cicero)