The Ukrainian visa is NO required for citizens of:
Austria, Belgium, Bulgaria, Canada, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Japan, Latvia, Lithuania, Luxembourg, Malta, Norway, Poland, Portugal, Principality of Andorra, Principality of Liechtenstein, Principality of Monaco, Republic of Iceland, Romania, San Marino, Slovakia, Slovenia, Spain, Sweden, The Holy See (State of the Vatican City), The Netherlands, The Swiss Confederation, United Kingdom, United States of America.
They are allowed to stay in Ukraine up to 90 days over a 180 day period holding a valid passport if the purpose of your journey is: tourism, private visit or business.
For different purposes (ex. immigration, work in Ukraine, etc) or, in general, longer stays visa is required.
No visas are required for citizens of Mongolia and the countries of the Commonwealth of Independent States (except Turkmenistan).
For the latest news consult the Ukrainian consulate in your country.
Possible re-introduction of the Visa regime for the citizen of EU, US and other countries.