English uses in for almost every place: in Rome, in Italy, in Europe. Italian splits this into two prepositions. For a city it uses a: a Roma, a Parigi, a Londra. For a country or a region it uses in: in Italia, in Francia, in Germania.
English speakers tend to reach for in every time, so in Roma is one of the most common beginner slips. The good news is that the choice depends only on the kind of place. It does not change with the verb, so the same preposition works whether you live somewhere or travel there.
Word list
CinafA1Chinain Cina = in/to ChinaEuropafA1Europein Europa = in/to EuropeFranciafA1Francein Francia = in/to FranceGermaniafA1Germanyin Germania = in/to GermanyInghilterrafA1Englandin Inghilterra = in/to EnglandItaliafA1Italyin Italia = in/to ItalySpagnafA1Spainin Spagna = in/to SpainAfricafA2Africain Africa = in/to AfricaAntartidefA2Antarcticain Antartide = in/to AntarcticaArgentinafA2Argentinain Argentina = in/to ArgentinaAsiafA2Asiain Asia = in/to AsiaAustraliafA2Australiain Australia = in/to AustraliaBrasilemA2Brazilin Brasile = in/to BrazilCanadamA2Canadain Canada = in/to CanadaGiapponemA2Japanin Giappone = in/to JapanGran BretagnafA2Great Britainin Gran Bretagna = in/to Great BritainIndiafA2Indiain India = in/to IndiaMessicomA2Mexicoin Messico = in/to MexicoNordamericaA2North Americain Nordamerica = in/to North AmericaOlandafA2Netherlandsin Olanda = in/to Netherlands, HollandPortogallomA2Portugalin Portogallo = in/to PortugalRussiafA2Russiain Russia = in/to RussiaSud AmericamA2South Americain Sud America = in/to South AmericaBelgiomB1Belgiumin Belgio = in/to BelgiumCentroamericamB1Central Americain Centroamerica = in/to Central AmericaCorea del SudfB1South Koreain Corea del Sud = in/to South KoreaEgittomB1Egyptin Egitto = in/to EgyptGreciafB1Greecein Grecia = in/to GreeceIrlandafB1Irelandin Irlanda = in/to IrelandLondrafB1Londona Londra = in/to LondonOceaniafB1Oceaniain Oceania = in/to OceaniaParigifB1Parisa Parigi = in/to ParisSvizzerafB1Switzerlandin Svizzera = in/to SwitzerlandTurchiafB1Turkeyin Turchia = in/to Turkey (country)AustriafB2Austriain Austria = in/to AustriaCatalognafB2Cataloniain Catalogna = in/to CataloniaColombiafB2Colombiain Colombia = in/to ColombiaCorea del NordfB2North Koreain Corea del Nord = in/to North KoreaDanimarcafB2Denmarkin Danimarca = in/to DenmarkFinlandiafB2Finlandin Finlandia = in/to FinlandGroenlandiafB2Greenlandin Groenlandia = in/to GreenlandIndonesiafB2Indonesiain Indonesia = in/to IndonesiaIsraelemB2Israelin Israele = in/to IsraelNorvegiafB2Norwayin Norvegia = in/to NorwayPakistanmB2Pakistanin Pakistan = in/to PakistanPechinofB2Beijinga Pechino = in/to BeijingPoloniafB2Polandin Polonia = in/to PolandRomafB2Romea Roma = in/to RomeScandinaviafB2Scandinaviain Scandinavia = in/to ScandinaviaScoziafB2Scotlandin Scozia = in/to ScotlandSingaporemB2Singaporea Singapore = in/to SingaporeSveziafB2Swedenin Svezia = in/to SwedenThailandiafB2Thailandin Thailandia = in/to ThailandUngheriafB2Hungaryin Ungheria = in/to HungaryViennafB2Viennaa Vienna = in/to ViennaArabia SauditafC1Saudi Arabiain Arabia Saudita = in/to Saudi ArabiaArmeniafC1Armeniain Armenia = in/to ArmeniaBielorussiafC1Belarusin Bielorussia = in/to BelarusBulgariafC1Bulgariain Bulgaria = in/to BulgariaCambogiafC1Cambodiain Cambogia = in/to CambodiaCechiafC1Czech Republicin Cechia = in/to Czech RepublicCroaziafC1Croatiain Croazia = in/to CroatiaEstoniafC1Estoniain Estonia = in/to EstoniaFirenzefC1Florencea Firenze = in/to Florence (city)IranmC1Iranin Iran = in/to IranLettoniafC1Latviain Lettonia = in/to LatviaLituaniafC1Lithuaniain Lituania = in/to LithuaniaLussemburgomC1Luxembourgin Lussemburgo = in/to LuxembourgMalesiafC1Malaysiain Malesia = in/to MalaysiaMaroccomC1Moroccoin Marocco = in/to MoroccoMongoliafC1Mongoliain Mongolia = in/to MongoliaMoscafC1Moscowa Mosca = in/to MoscowNuova ZelandafC1New Zealandin Nuova Zelanda = in/to New ZealandPerùmC1Peruin Perù = in/to PeruRomaniafC1Romaniain Romania = in/to RomaniaSerbiafC1Serbiain Serbia = in/to SerbiaSlovacchiafC1Slovakiain Slovacchia = in/to SlovakiaSloveniafC1Sloveniain Slovenia = in/to SloveniaSudafricafC1South Africain Sudafrica = in/to South AfricaTunisiafC1Tunisiain Tunisia = in/to TunisiaUcrainafC1Ukrainein Ucraina = in/to UkraineVeneziafC1Venicea Venezia = in/to VeniceAlbaniafC2Albaniain Albania = in/to AlbaniaAlgeriafC2Algeriain Algeria = in/to AlgeriaBoliviafC2Boliviain Bolivia = in/to BoliviaBruxellesfC2Brusselsa Bruxelles = in/to BrusselsEurasiafC2Eurasiain Eurasia = in/to Eurasia (supercontinent)IraqmC2Iraqin Iraq = in/to IraqKazakistanmC2Kazakhstanin Kazakistan = in/to KazakhstanVietnammC2Vietnamin Vietnam = in/to Vietnam
How it works
Ask yourself one question: is this place a city or a country? A city takes a. A country or a region takes in. Italian uses the same preposition for being somewhere (sono a Roma, I am in Rome) and for going there (vado a Roma, I am going to Rome). English switches between in and to, but Italian keeps one word for both.
Vivo a Roma, in Italia.
(I live in Rome, in Italy.)
Andiamo a Parigi, in Francia.
(We're going to Paris, in France.)
Notice that there is no article. You say in Italia, not nell'Italia, and a Roma, not alla Roma.
The words
Cities take a
This group covers Roma, Parigi, Londra, Firenze, Venezia, Vienna, Bruxelles, Mosca and Pechino. Every city works the same way, whether it is big or small, Italian or foreign.
Mia sorella lavora a Londra.
(My sister works in London.)
Domani andiamo a Firenze in treno.
(Tomorrow we're going to Florence by train.)
Sono stato a Venezia, a Vienna e a Bruxelles.
(I've been to Venice, Vienna and Brussels.)
Il volo per Pechino fa scalo a Mosca.
(The flight to Beijing stops over in Moscow.)
European countries take in
This group covers Italia, Francia, Germania, Spagna, Portogallo, Inghilterra, Gran Bretagna, Irlanda, Belgio, Olanda, Svizzera, Austria, Polonia, Cechia, Ungheria, Svezia, Norvegia, Danimarca, Finlandia, Grecia, Turchia, Russia and Ucraina. Masculine countries such as Portogallo and Belgio follow the same rule as feminine ones.
Quest'estate andiamo in Spagna o in Portogallo.
(This summer we're going to Spain or Portugal.)
Marco studia in Germania.
(Marco studies in Germany.)
Fa molto freddo in Norvegia e in Finlandia.
(It's very cold in Norway and Finland.)
Countries further away and regions also take in
This group covers Cina, Giappone, India, Canada, Messico, Brasile, Argentina, Australia, Egitto, Marocco and Tunisia. Regions work the same way: in Catalogna, and inside Italy in Toscana and in Sicilia.
I miei cugini abitano in Canada.
(My cousins live in Canada.)
Vorrei andare in Giappone in primavera.
(I'd like to go to Japan in spring.)
Barcellona è in Catalogna.
(Barcelona is in Catalonia.)
Watch out
The typical mistake is in Roma or in Londra. If the place is a city, switch to a.
Treat this as a strong default, not an absolute law. There are a few exceptions:
Small islands behave like cities: a Cuba, a Cipro, a Capri. Large islands behave like regions: in Sicilia, in Sardegna.
Plural country names take a preposition combined with an article: negli Stati Uniti.
Modified country names also need the article: nell'Italia del Nord (in northern Italy).
These article forms follow their own rules. For everyday sentences, the simple rule is enough: a for the city, in for the country.
Summary
For cities, use a: a Roma, a Parigi, a Londra. For countries and regions, use in with no article: in Italia, in Francia, in Toscana. The same preposition covers being there and going there. Remember the few exceptions: small islands take a (a Cuba), and plural or modified names take an article (negli Stati Uniti).