- Andorra (468 sq. km.)
- Tuvalu (26. sq. mi)
- Marshall Islands (181 sq. km.)
- Palau (459 sq. km.)
- Nauru (21 sq. km.)
- Vatican City (0.44 sq. km.)
- Monaco (1.95 sq. km.)
- Seychelles (455 sq. km.)
- San Marino (61 sq. km.)
- Saint Kitt and Nevis (261 sq. km.)
A microstate is pretty much what it sounds like: a sovereign nation with either a very small population or very little land area, or both. Andorra is the largest of the microstates in terms of land mass; the largest by population appears to be Malta, which crams 407,000 people in a mere 316 sq. km.
Oh, and by the way, today is the anniversary of the ratification of the Lateran Treaty, which created the sovereign state of Vatican City.