Some of the most notable examples include:

1. Japan: Japan has one of the oldest populations in the world, and its birthrate has been in decline for decades. The country has struggled to reverse the trend, and its population is projected to decline by around 20% over the next few decades.
2. Italy: Italy has also seen a decline in birthrates, and its population is projected to decline by around 8% over the next few decades.
3. Greece: Greece has also seen a decline in population, particularly due to emigration and low birth rates, along with a decline in the death rate.
4. Ukraine: Ukraine has also seen a decline in population due to a combination of low birth rates and high mortality rates, and it is projected to decline further in the next decades.
5. Bulgaria: Like other Eastern European countries, Bulgaria has also experienced population decline in recent years, and the trend is expected to continue.
6. Romania: Romania is experiencing a decline in population caused by low fertility rates, high death rates, and emigration.

These countries, as well as many others, are facing significant economic, political, and social challenges due to their population decline, including a shrinking workforce and an aging population, which can affect the economy, healthcare and pensions systems, and can also impact society in other ways, and many countries have implemented policies to address these challenges.