According to the United Nations, Ukraine has a population of 36,744,636 as of 2023. In July 2023, Reuters reported that due to the refugee outpouring into Western Europe, the population of Kyiv-controlled areas may have decreased to as low as 28 million. This is a steep decline from 2020, when it had a population of almost 42 million people. This is in large part due to the ongoing Ukrainian refugee crisis and loss of territory caused by Russia's invasion of Ukraine. The most recent census of a post-Soviet Ukraine occurred over 20 years ago, in 2001. Thus, much of the information presented here could be inaccurate and/or outdated.

An ongoing refugee crisis began in Europe in late February 2022 after Russia's invasion of Ukraine. Over 6 million refugees fleeing Ukraine are recorded across Europe, while an estimated 8 million others had been displaced within the country by late May 2022. Approximately one-quarter of the country's total population had left their homes in Ukraine by 20 March. 90% of Ukrainian refugees are women and children, while most Ukrainian men between the ages of 18 and 60 are banned from leaving the country. By 24 March, more than half of all children in Ukraine had left their homes, of whom a quarter had left the country. The invasion caused Europe's largest refugee crisis since World War II and its aftermath, is the first of its kind in Europe since the Yugoslav Wars in the 1990s, as well as the fourth largest refugee crisis in history, and is the largest refugee crisis of the 21st century, with the highest refugee flight rate globally.