This is just a synthetic overview of a very complex issue; we strongly recommend reading the sources (mettere # ID).
Every Italian law about immigration is based on a previous one, which is why a little history is needed. If you’re not interested, jump directly to the Bossi-Fini Law and the Security Set, the current laws (METTERE # ID). Every law gets its name from its promoters.

• Law 39/1990 Legge Martelli.
  It treats the immigration issue by narrowing the flow of immigration, giving a pre-set number of accesses (a quota) and linking them to the job market. A permit of stay, which lasts two year and is renewable, can be obtained for work, study, medical care or family reunification. Those that get in with regular documents but stay after the expiration of the permit, or those exceeding the quota, are considered “illegal immigrants”. Illegal and irregular immigrants, as well as the ones who do not have the required qualifications, are expelled. Expelled immigrants have 15 days to leave Italy on their own, otherwise they will be deported by police.
  The aim of this law was the regularisation of immigrant workers, who were exploited as irregular workers. This law did not create an organic program for the future, but an economic view of immigration, which remains a constant of Italian immigration legistlation.

• Law 40/1998 Legge Turco-Napolitano.
  This law provides a permanent residency permit (carta di soggiorno), regulates the process to get it and also to get Italian citizenship. Temporary detention centres for illegal and irregular immigrants (CPT) were created by this law. CPTs are where people who will be forcedly deported (as determined by the Legge Martelli) are placed. Immigrants who must be identified and asylum seekers are also placed in the CPTs, but temporarily.

• Law 189/2002 Legge Bossi-Fini.
  This law tightens the norms against the aiding and abetting of illegal immigrants. Immigrants found in international waters, formerly outside of the patrolling power of Italy, can be sent back to their country or to neighbouring countries. No boat carrying people without visas can dock on Italian coasts. To obtain a work permit – “contract to stay as a dependent employee” – a work-contract and a rental agreement are needed.
  Forced detention – and no longer the intimation of detention – becomes ordinary rule: all illegal/irregular immigrants found by police on Italian ground without the necessary documentation must be identified and deported to their countries of origin. Migrants can be detained in a CPT for up to 60 days. They can only come back to Italy after 10 years have passed. Non-Italian citizens serving a two-year punishment can, instead, be deported. The system of protection for asylum-seekers and refugees (the so-called SPRAR) is introduced.
  The requirements that immigrant workers in dependent employment must meet in order to qualify for regularisation are as follows:
  - the workers must have been employed by a company for at least three months;
  - the employer must commit itself to hiring the worker on an open-ended contract, or on a fixed-term contract lasting at least one year;
  - the employer must pay the workers at least EUR 700 per month, plus EUR 100 in expenses, and all within 10 days of the submission of the application for regularisation and of the relevant documentation.

• Criticisms of the Bossi-Fini law:

-Forced deportation in international waters contravenes Article 13 of the Universal Declaration of Human Rights of 1948: “Every man is free to leave his land”; it is also against the Geneva Convention of 1951, as many refugees are sent back instead of being offered protection; it involves the risk of shipwreck in the sea, meaning that it is also against human rights.

-Having documents can make it easier for police to send an immigrant to his/her country; this encourages immigrants to “lose” their documents or give false names and nationalities (making police work more difficult and expensive), and to remain in the CIE as long as possible.

-Life conditions in CIE are hard. Indeed, several immigrants organised riots, escaped, or tried to commit suicide.

-No information was given about healthcare policies or regulation in the CIE.

-It is now impossible to regularise the situation of immigrant workers who have received a deportation order but remain in Italy. Many firms employ immigrant workers in this category, and the impossibility of regularising their situation risks leaving many companies with an insufficient number of workers.

-Employers now bear a great social responsibility for defining a welcoming policy for immigrants. Employers, in fact, will have to guarantee a decent life to immigrant employees. In reality, however, employers will have the power to blackmail and exploit illegal immigrants.

-Without the signing of joint agreements with the countries from whose coasts these immigrants embark, forced returns will hardly be effective.

-Push-backs are often violent acts, as the immigrants refuse to be repatriated. Two cases are the Tunisian citizens tied with tape and the Libyan immigrant pushed back in 2009

-Despite the fact that 92% of the legal immigrants come with family reunion visas and working visas, the Bossi-Fini law focuses mostly on illegal migration: only 5 out of 38 articles deal with family reunion and work policies. The government has no actual policy regarding the social integration of regular immigrants (religious dialogue, for example).

• Security Set 94/2009: Illegal immigration becomes a crime, thus all public officers and public workers must report the presence of an illegal immigrant. Illegal immigrants are liable to pay a fine and can now be detained by the authorities for more than six months.
  Each petition made to the public administration, such as requests for money transfers, much be accompanied by one’s permanent residency permit, with the exception of applications for health care, school and birth certificates.
  Helping an illegal immigrant come to Italy, or housing undocumented migrants is now prosecutable as a crime (up to 3 years in prison). Italian teachers must report undocumented children. School drop-out rates are increasing as a result.
  Legal immigrants married to an Italian must wait two years in order to get Italian citizenship.
  The law allows for the formation of unarmed citizen patrol groups.
  Finally a difference between CDA, CARA and CIE is introduced.

• In April 2011 Roberto Maroni, ex-Interior Minister, issued a ministerial circular letter that forbids reporters and journalists access to any detention centre. The new Interior Minister Anna Maria Cancellieri revoked the circular letter. As of 23 April 2012, access should be granted.

• On 20 April 2012 Italian Government established the quota for seasonal workers: 35,000 units from 23 non-EU countries, 4,000 more are admitted in advance if they have completed education and training.

Sources:
[en] Geneva Graduate Institute, "Global Detention Project:Italy", 2011
[en] Silvia Rusconi, "Italy´s migration experiences", 2010.
[en] E. Komada, "Turned away. The detrimental effect of Italy’s public security law on undocumented children’s right to education", Boston Uni Law Journal, 2011. Italy’s violation of the Convention on the Rights of the Child denying education to undocumented children. Also provides a history of Italian immigration law.
[en]European Industrial relations observatory on-line, "Law 189/2002, or Bossi-Fini", 2002
[en]Italy’s immigrants despair at new laws - BBC. (Security Set 94/2009)
en fr es sr sq ro ar Editorial, Interviews, Official analysis and reports on right of citizenship