Overall, the rules of capitalization are very similar in English and in Spanish. Capitalization is used in three basic ways:
1. To indicate the beginning of a sentence.
2. To distinguish proper names.
3. In titles of books, movies, lectures, and so on; in headers.
What is a “proper name”?
A proper name is what something or someone is named, as opposed to what it is. In the following pairs, the first is a proper name: John/boy, Barcelona/city, Mrs. MacDuff/teacher, and so on.
The first rule should be pretty clear. Be sure to capitalize the first word of every new sentence, just as you do in English.
The second rule, which deals with proper names, is also pretty similar in English and in Spanish. Names of people, cities, and countries are capitalized in both languages:
Me llamo Benicio Juan Armandez.
My name is Benicio Juan Armandez.
Vivo en Buenos Aires, la capital de Argentina.
I live in Buenos Aires, the capital of Argentina.
Brand names are also considered proper names:
Prefiero las zapatillas de deportes marca Nike.
I prefer Nike sneakers.
Titles and Headers
However, the third rule of capitalization isn't exactly identical in English and Spanish. In English, we generally capitalize most of the words in a title or header (the exceptions being prepositions shorter than six letters and articles, although these rules may vary). In Spanish, only the first word of the header or title is capitalized:
El autor de la novela Cien años de soledad es Gabriel García Márquez.
The author of the novel A Hundred Years of Solitude is Gabriel García Márquez.
El primer capítulo de este libro se llama “Bienvenidos al mundo del idioma castellano”.
The first chapter of this book is called “Welcome to the World of Spanish.”
¿Has visto la película Tráfico?
Have you seen the movie Traffic?
That's All for Spanish
This pretty much takes care of capitalization in Spanish. Although we have additional capitalization rules in English, none of them apply in Spanish.
Days of the Week
In Spanish, the days of the week are written in lowercase letters: lunes, martes, miércoles, jueves, viernes, sábado, domingo (Monday, Tuesday, and so on).
Months of the Year
The same is true of the twelve months of the year: enero, febrero, marzo, abril, mayo, junio, julio, agosto, septiembre, octubre, noviembre, diciembre (January, February, and so on).
In Spanish, title abbreviations like Sr. (Mr.) and Dr. (Dr.) are capitalized, but written out titles are not: señor García, doctor Sánchez, doctora Flores. Also note that for the feminine title doctora, the abbreviation is Dra.
Languages and Nationality
It is unnecessary to capitalize languages and nationalities:
Yo soy rusa. Hablo ruso, inglés y castellano.
I am Russian. I speak Russian, English, and Spanish.
¿Se habla francés en Canadá?
Is French spoken in Canada?
Finally, don't worry about capitalizing names of religions:
Soy judía; mi religión es judaísmo.
I am Jewish; my religion is Judaism.
La religión más común entre los latinos es el catolicismo.
The most common religion among Latinos is Catholicism.