Dual citizenship may offer greater freedom, but some countries have strict rules against holding two nationalities.
Countries including China, India, Japan and Singapore have some of the toughest restrictions on dual citizenship.
In some cases, citizens who voluntarily obtain another nationality can lose their original citizenship.
India does not recognise dual citizenship, but offers Overseas Citizenship of India, or OCI, status to eligible people of Indian origin.
Other countries may allow dual citizenship only in limited circumstances, such as through birth, descent or special government approval.
Experts say anyone planning to obtain a second passport should carefully check the citizenship laws of both countries before making a decision.
