Viking Knives

The term "Viking" dates back to early Scandanavian language, believed to be derived from the word Vikingr,  which means 'pirate'. These violent raiders traveled by sea and became know for pillaging neighboring villages and then onward to other countries along the coast of northwest France and Britain. Although records indicate they dated back to the 8th century, they were very advanced in their weaponry techniques and blacksmithing. Two knives have been identified as weapons that were predominantly used by the Vikings.

Viking Knifr

One is the knifr which was a plain, single edged blade with the tang running through the handle (this one is made of bone).This was a common weapon that even slaves were allowed to carry because it played an important role in everyday Scandinavian life. The larger versions were used as hunting knives while smaller ones were utilized as an everyday tool. Because these knives were allowed to be used by everyone, they were often found in burial graves of not only men, but also women and children. 

Broken-back seax

The other type is known as a seax, traditionally known as a "broken back" style of knife. It's a much larger and heavier knife often used like a machete. These were less common though and used by the upper class, wealthier Vikings with much larger versions serving more like a sword, only much easier to use and produce than a traditional sword. The tang seems to have been longer throughout the long handle which may indicate two handed use. Although they don't seem to be very common in Scandinavia, these sword-like knives seemed to flourish around the settlements of England & Ireland. 

Sources: 

By BabelStone (Own work), CC0, https://commons.wikimedia.org/w/index.php?curid=10771702

http://www.historyworld.net/wrldhis/PlainTextHistories.asp?historyid=ab86

https://en.wikipedia.org/wiki/Viking_Age_arms_and_armour