It's often been said that tax evasion is something of a national sport in Italy. More recently, the government has begun to crack down on tax evasion (and avoidance), introducing tough new measures. As a result, many small businesses are coming out of 'nero' (literally, 'the black', meaning the untaxed black market), and declaring themselves legitimately. It's still early days, but it does seem that Italy may be taking the first steps towards leaving its old reputation behind.
If you are going to live, work, or set up in business there, then this is something you will need to take professional advice on: it rather falls outside the scope of any general tourist website. As a first port of call, you could look at the English pages on Italian taxes from the Italian government, at agenziaentrate.gov.it.