Portuguese is similar in many ways to Spanish, but there are enough differences, in both writing and speech, so that a speaker of one may require some practice to effectively understand a speaker of the other. Compare, for example:
(Both translate as "She always closes the window before having dinner.")
Portuguese speakers are generally able to read Spanish Castilian, and Spanish Castilian speakers are generally able to read Portuguese, even if they can't understand the spoken language. The Portuguese varieties spoken in Portugal are closely related to the Galizan (or "Galician") varieties of the language. Tourists in Portugal should note that trying to communicate with the locals in Spanish may seem offensive.
Brazilian Portuguese is the same language as in Portugal. However, a few words and expressions are written differently (like 'bus' - "ônibus" (Braz.) = "autocarro" (Port.) ). Galizan Portuguese is generally strongly Castilianized.
In some places, Spanish and Portuguese are spoken almost interchangeably. There is a town on the Brazil/Paraguay border, for example, known in Brazil as Ponta Pora and in Paraguay as Pedro Juan Caballero, where conversations regularly switch back and forth between the two languages. (To add to this rich diversity, many people in the region also speak Guarani.). Portuguese/Spanish daily bilingualism is also common in Galiza.
Speakers of other Romance languages may find a peculiarity in the conjugating of certain apparently infinite verbs. In particular, when constructing a future tense or conditional tense expression involving an indirect object pronoun, the pronoun is placed between the verb stem and the verb ending. For example, Dupondt said trazer-vos-emos o vosso ceptro. Translating as literally as possible, this is "bring (stem)-to you (formal)-we (future) the your sceptre". In English we would say, "We will bring you your sceptre."