The Centers for Disease Control (CDC) recommends that travelers avoid all nonessential international travel because of the COVID-19 pandemic. Many countries are implementing measures to help slow the spread as well as prevent their own health care systems from becoming overwhelmed. These measures may differ by region and often include travel restrictions, mandatory quarantines, prohibiting non-citizens from entry, etc. Please refer to the CDC's FAQ About International Travel for further information.
In addition to the FAQ resources, the CDC has created a web map intended to show COVID-19 Travel Recommendations by Country that may be useful.
For individuals returning from international travel within the past 14 days, refer to the CDC's guidelines - including steps to monitor your health and practice social distancing.