How strong is your travel document?

While immigration and border control are the proverbial doors of a state, passports are the keys; and not all these keys are made equal.

Whether it’s visa on arrival versus visa applications, or visa requirements being waived entirely, some passports simply open more doors more quickly and painlessly than others. Not only do they open them, but they can help keep them open for you and your kin too. Long term residency rights, spousal visas and even citizenship can hinge at least in part on what passport you hold.

Because of this, it’s valuable to know what privileges your passport affords you if you’re planning to move abroad. It’s also necessary as part of understanding how straightforward your residency application will be, and how easily the same passport can facilitate travel to the neighboring states too.

Immigration rules, quotas and family visa entries have all been making headlines in both the U.S. and the U.K. recently, but it’s important to understand that aspects of immigration law and regulation have always been an uneven playing ground, depending in part on which travel document you hold.

The disparity between a “good” passport and a “bad” one is striking when you look at it from best to worst. The Singaporean passport, held by some four million citizens, offers visa-free access to 127 countries. Whereas Afghanistan’s passport offers visa-free access to just five. Instead, Afghan citizens must engage in long, often arduous and complex visa application procedures. This range illustrates just how much value a passport can offer.

Curious about the value of your own passport? There are many indices, but one of the best is the Global Passport Index (GPI).

So why do some passports open more doors than others? This is a multifaceted answer; countries obtain better access rights for their citizens through bilateral negotiations for the most part. As a result, visa/visa-free access arrangements are often reciprocal, i.e. “you give me visa-free access, and I’ll do the same for you.”

In certain situations, a more powerful country, especially those with significant investments in the negotiating partner, has more leverage. It’s also a general rule of thumb that less secure or safe states, with a risk of or actual civil strife, will see the access rights of its citizens limited for obvious reasons.

It’s not all Machiavellian machinations though, in no small part a passport’s effectiveness is a function of a state’s relationship with the rest of the world. It’s no surprise that states like Singapore, which are involved in very few, if any, international disputes, generally find themselves so well received.

Serbia has done an excellent job at negotiating visa-free travel with its neighbors. Shooting up various passport indexes. Serbia secured visa-free travel to the E.U. states in 2009. Making it one of only three countries in the world that can visit Europe, Russia and China without a visa. If you consider the lengthy processes involved in procuring Russian and Chinese visas for British and American citizens (both of whose passports rank above Serbia’s) this is no small feat!