Some countries consider multiple citizenship undesirable and take measures to avoid it. Since a country only has control over who has its citizenship, but has no control over who has any other country’s citizenship, the only way for a country to avoid multiple citizenship is to deny its citizenship to people in cases when they would have another citizenship. This may take the following forms:

• Automatic loss of citizenship if another citizenship is acquired voluntarily (such as Azerbaijan, China, Czech Republic, Denmark, India, Indonesia, Japan, Kazakhstan, Nepal, the Netherlands, Norway).
• Possible (but not automatic) loss of citizenship if another citizenship is acquired voluntarily (such as Singapore, Malaysia, South Africa).
• Possible (but not automatic) loss of citizenship if people with multiple citizenships do not renounce their other citizenships after reaching the age of majority or within a certain period of time after obtaining multiple citizenships (such as Japan and Montenegro.)
• Denying automatic citizenship from birth if the child may acquire another citizenship automatically at birth.
• Requiring an applicant for naturalization to apply to renounce his/her existing citizenship(s), and provide proof from those countries that they have renounced citizenship, as a condition of naturalization.
• Some countries have more complex rules on dual and multiple citizenship.