concratulazioni=contratulations complimenti=compliments congratulazioni it is used only when someone has reached a goal complimenti it is used for example to say: "sei bellissima, complimenti" (you are beautiful, compliments) and for the reason of concrats aswell

/felicitazioni/ (usually expressed in the plural form) stems from felicita` (happiness) and means: I express you my happiness regarding XYZ where XYZ is usually something like: -- new born baby -- marriage Something that is 'happy' in the eyes of Mother Nature. You use /congratulazioni/ when you are expressing your consideration towards something (also usually related to happiness) but measured on the scale of social events or of a scientific discovery or an invention. /complimenti/ is when you see somebody behaving in quite a good way, or soembody whi went successfully through an examination, something not really great but where the person shined. For instance, if you see somebody that with his behaviour (even in something small) might be an example for yourself, you can say to this person: -- complimenti per aver fatto XYZ, mi ha offerto un buon esempio, grazie. An interesting question, complimenti sinceri!