All countries
Do Canada, Ireland and Italy Allow Dual Citizenship?
Canada: yes
IRCC says Canadians are allowed to take a foreign citizenship while keeping their Canadian citizenship. You don't apply for dual citizenship, and there's no certificate for it. Source: IRCC Help Centre IRCC also notes that every country decides whom it considers a citizen. Source: IRCC
Ireland: yes
Ireland's immigration service says that under Irish law you don't have to give up another citizenship to claim Irish citizenship by birth, descent or other reasons, or to naturalize. Source: Irish Immigration Service Delivery You also don't have to give up Irish citizenship to become a citizen of another country, but some countries' laws may require you to renounce it. Source: Irish Immigration Service Delivery
Italy: yes, with a 2025 catch
Italy's Foreign Ministry says the 1992 citizenship law (Law 91/1992) recognizes the right to hold more than one citizenship. Since August 16, 1992, acquiring a foreign citizenship doesn't cause loss of Italian citizenship unless you formally renounce it. Source: Italian Foreign Ministry
But for citizenship by descent, holding another citizenship now matters. Under the 2025 law, people born abroad who hold another citizenship aren't deemed to have acquired Italian citizenship automatically unless an exception applies. Examples are a parent or grandparent who held only Italian citizenship, or a parent who lived in Italy for two continuous years after becoming Italian and before your birth. Source: Italian Foreign Ministry See the "only Italian citizenship" route.
The U.S., Germany and Poland
See Can you hold dual citizenship with the U.S. and another country? and Germany's 2024 change.