Depending on what two countries you hold passports in:
Crossing boarders:
Finally as long as you understand what countries your passports are welcome in, there will be no trouble, so don't sweat it.
Being a citizen of two countries.
If it's a valid US passport or you are a dual-citizen most likely
If you are a citizen of both countries and that their laws allow for a dual citizen then yes it is possible to hold both passports.
Maybe there is dual citizenship, but you need to contact passport services to find out.
If you have both citizenship and both their laws allow you to hold both passport then you are legally a dual citizen of the countries.
If you are a citizen of both countries then you can apply for the dual citizenship so that you can get both passports.
You cannot change your passport. Rather, you can apply for a dual citizenship passport, meaning you will be issued another passport if you are eligible as a citizen of that particular country
You must always use a valid American passport when entering and departing the US even if you are a dual citizen.
only if a US citizen has dual citizenship with another country, than you can have a passport for each country.
The rules of dual citizenship are quite easy to understand. Most countries neither deny or recognizes dual citizenship. However, if you are a dual citizen you must enter the country with the country's passport you own.
You can hold a passport in any country you are a citizen of however, if you have dual citizenship you need to be sure both countries allow for dual citizenship.
You must move to Mexico with your spouse and live there for two years with an immigrant visa, then you can apply for Mexican citizenship. You can have both a Mexican and a US passport and be a dual citizen. If you were not married to a Mexican citizen, you would have to live there for four years.