several of the previous proz answers are wrong

competenza economica is the "matching" principle

competenza temporale is the "accruals" principle

If you need sources, let me know

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Note added at 1 hr (2007-04-28 20:54:56 GMT)
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Competenza temporale: i costi e i ricavi sono imputabili all’esercizio se sono maturati nel periodo, a prescindere dal fatto che nel corso dell’esercizio sia avvenuta la relativa manifestazione numeraria (incasso o pagamento).

Competenza economica: i costi si considerano di competenza se sono correlati ai ricavi dell’esercizio.

Following is an outdated list of the major accounting principles (from an old US accounting text), but it gives you the idea.

If you go here (http://www.accountingbase.com/AcctPrinciples1.html) you can read a very simplified but clear description of what the accruals and matching principles are and compare them with the Italian descriptions above.

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Note added at 1 hr (2007-04-28 20:55:49 GMT)
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The Principles

1. The Accrual principle
2. Historical cost principle
3. Consistency Principle
4. Prudence Principle
5. Materiality Principle
6. Matching Principle
7. Going Concern Concept
8. Conservative Principle
9. Separate Legal Entity Concept

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Note added at 1 hr (2007-04-28 21:02:04 GMT)
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And don't confuse the principio della competenza temporale and the principio della competenza economica with the principio della competenza finanziaria (quante competenze questi italiani!?) ;-)