Y-DNA Haplogroups are various groupings based on similar genetic markers.  They are associated with early human migration which can be traced to various geographical regions.  These haplogroups relate to deep ancestry which can go back 2,000 to 50,000 years; they are an indicator of the long range journey that a direct paternal ancestor has taken.  The Y-chromosome is passed down directly from father to son.

Haplogroups do not reveal anything about your current ethnic background, physical characteristics, or family genetics.  This is due to the Y chromosome making up only a very small proportion of the genetic material; less than 0.1%.  Thus 99.9% of a persons genes will be a melting pot of several hundred family ancestors.  As an example, a persons DNA will be derived from a pool of 512 ancestors who lived ~300 years ago (10 generations).

Excellent information on haplogroups can be found on this website:
European Haplogroups and Subclades

The following information and maps are from the Eupedia website listed above.

R1b is the most common haplogroup in Western Europe, reaching over 80% of the population in Ireland, the Scottish Highlands, western Wales, the Atlantic fringe of France and the Basque country.  It originated in the Middle East / Anatolia around 8,000 years ago and expanded into Europe through the Balkans and Danube Valley.

Haplogroup E3b (E1b1b) represents the last major migration out of North Africa into Europe.  There are 3 main subgroups (subclades); V13, V22, and V12.  E-V13 is the most common subgroup and is associated with ancient Greek expansion and colonisation.  E-V12 is a common subclade in Egypt and is predominantly found in the Upper Nile, near Luxor (Thebes, the capital of ancient Egypt).

Haplogroup I2 may have originated in south-eastern Europe some 17,000 years ago and developed into four main subgroups: I2a1, I2a2, I2b1 and I2b2.  I2b is found throughout Western Europe. Nowadays, I2b peaks in central and northern Germany (10-20%), the Benelux (10-15%) as well as in northern Sweden.  It is also found in 3 to 10% of the inhabitants of Denmark, East England, and Northern France.