The Istro-Romanians (Istro Romanian: rumeri or rumâri) are a Romance ethnic group native to or associated with the Istrian Peninsula. Historically, they inhabited vast parts of it, as well as the western side of the island of Krk until 1875. However, due to several factors such as the industrialization and modernization of Istria during the socialist regime of Yugoslavia, many Istro-Romanians emigrated to other places, be they Croatian cities such as Pula and Rijeka or places such as New York City, Trieste and Western Australia. The Istro-Romanians dwindled severely in number, being reduced to eight settlements on the Croatian side of Istria in which they do not represent the majority.

It is known that the Istro-Romanians are not descendants of a historical Roman population native to Istria, since the differences between the Istro-Romanian language and the geographically close, now extinct Dalmatian language, are notable. Additionally, similarities to Transylvanian Romanians and Timok Vlachs suggest that Istro-Romanians may originate from areas west of Romania or Serbia. Although it is not known exactly how and when, the Istro-Romanians settled in Istria, where they would remain for centuries until they began to assimilate. Even now, with several associations and projects aiming to preserve their culture and with the support from both the Croatian and Romanian governments, the Istro-Romanians are not officially recognized as a national minority.

Although it has become widely popular and is now used almost exclusively, the term "Istro-Romanian" is a somewhat controversial scientific invention, which is not used by them to self-identify. The Istro-Romanians prefer to use names derived from their native villages, which are Jesenovik, Kostrčani, Letaj, Nova Vas, Šušnjevica, Zankovci, the Brdo area and the isolated Žejane. Others also use "Vlach", but to refer to the entire Istro-Romanian population, the names rumâri and rumeri are often employed. Their language is highly similar to Romanian, both being part of the Eastern Romance languages family alongside Aromanian and Megleno-Romanian, all descending from Proto-Romanian. However, Romania regards these ethnic groups as part of a "broad definition" of what a Romanian is, which is debatable and does not have a widely accepted view.

The Istro-Romanian culture has costumes, dances and songs with many similarities to those of Romania. Literature in Istro-Romanian is small, with the first book published in 1905. Historically, they were peasants and shepherds, with many of them being poor and without having received education until the 20th century. Today, the Istro-Romanian language has little use in education, media and religion, with Croatian imposing itself in these and other domains. They are so few that they have been described as "the smallest ethnolinguistic group in Europe". It is thought that if their situation does not change, the Istro-Romanians will disappear in the following decades.

The term "Istro-Romanian" is commonly used among researchers and linguists to identify this Eastern Romance people from the Istrian Peninsula. However, it is a relatively recent creation from the middle of the 19th century based on geographic rather than scientific criteria. This denomination was used for the first time by the Romanian writer and historian Gheorghe Asachi (as istroromâni), and then by the Slovene philologist Franz Miklosich, (as istrischen Rumunen and istro-rumunisch), from which the name of the Istro-Romanian language and its speakers would be generalized. Nowadays, it is almost exclusively employed, and highlights the similarity of this language with the Romanian one. However, the Istro-Romanians do not identify with this name, and the use of "Istro-Romanian" outside the context of linguistics can be controversial until a certain point. Some people use the more recent name "Vlashki and Zheyanski language".

To refer to themselves as a whole, the Istro-Romanians may use rumâri, derived from the Latin romanus. The similar rumeri is also used since the 17th century, but this endonym (internal name, used by the ethnic group in question) does not appear in documents until its reuse by the Istro-Romanian writer and professor Andrei Glavina and the Romanian historian Constantin Diculescu and then by the Romanian journalist and professor Alexandru Leca Morariu in the 20th century. Due to the influence of Romanian researchers, Istro-Romanians also use the Croatian word rumunji, especially in contact with foreigners. Given the weakness of Istro-Romanian national sentiment, some elder people call themselves Romanians or Romanian-speaking Croats or even Italians (except in Žejane) to differentiate themselves from the surrounding Croats.

Many Istro-Romanians prefer to use a demonym derived from the name of their native village. For example, those from Šušnjevica use șușnevți and șușnevski or šušnjevski for their language, those from Nova Vas use novosani and novosanski or novošånski for their language, those from Kostrčani use costărčånți and those from the Brdo area use brijånski for their language. Generally, the Istro-Romanians from the villages south of the Učka mountain range also use the name vlåš (singular vlåh) and vlaška or vlaški for their language, taken from the South Slavic word "Vlach". On the other hand, in the northern village of Žejane, the only other one in which Istro-Romanian is spoken, jeianți or žejånci is used for the people and jeianski, žejanski or po jeianski cuvinta for the language. Croats also call them jeianci or vlaski, but the inhabitants of Žejane do not identify as Vlachs.

The Istro-Romanians have been called in many ways by the peoples that lived alongside them or in their surroundings. One of the earliest exonyms (external names) used for Istro-Romanians is Ćići, given by the Croats. It appears in Latin documents in the form of chichii, in Italian ones first in the form of chichi and later as cici or cicci, and in German ones as tschizen, tschitzen, zitschen, tschitschen, ziegen and zische.