Relativistic quantum mechanics

P111, P-111, or P.111 may refer to:

• P111, a highway in Latvia; see List of National Roads in Latvia#State 1st Class Roads
• P.111, a Spanish Navy patrol craft; see List of active Spanish Navy ships
• P.111, a Slovenian patrol boat; see Law enforcement in Slovenia
• $\mathfrak{P}$¹¹¹, a designation for Papyrus 111, a copy of the New Testament in Greek
• Boulton Paul P.111, a British experimental aircraft in use from 1950 to 1958
• Piaggio P.111, an Italian high-altitude research aircraft in use from 1941 to 1943
• Quita Suevo (P-111), a Colombian Navy patrol boat; see Asheville class gunboat

111P may refer to:

• 111P/Helin-Roman-Crockett, a periodic comet in our solar system