The Surname YDNA test is used to establish the genetic profile (haplotype) of deceased ancestors along one's direct paternal line (as indicated by the blue line in the pedigree image below).

The YDNA is passed largely unchanged from father to son. This YDNA inheritance pattern follows the passing of the surname common to many cultures; therefore, the YDNA is useful in discovering clues along one's paternal line. It is currently the most popular form of DNA testing.

The Y-chromosome. It is what makes all babies male and is a record of our ancestry carried with us for the next generation to keep.     

We inherit a Y-chromosome from our father, who in turn received his from his father and so on.

In fact, it can remain unchanged for many generations, so you will likely have the exact same Y-chromosome as your g-g-g-g-g-g-grandfather. You will also often share the same surname as it is passed down the very same line (which is why it is so useful to genealogists!)

In recent years, advances in genome research have enabled the cost of DNA testing to come well within the reach of genealogists. Given the amount of time and expense that most genealogists have devoted to their research, using DNA to break through brick walls is an excellent solution.

Y-DNA testing is at its most powerful when used with the existing paper records in trying to prove (or disprove) a theory or connection between two males with the same or similar surname. This can also be expanded to compare many males with the same surname as part of a Surname Project.