what is this ?

Whatever this is it has been slowly taking over my lawn and garden for the past 2 years and i'd love to get rid of it any ideas ?

Looks like Yarrow, a beautiful medicinal herb and companion plant. 

http://www.ashtreepublishing.com/Book_City_Herbal_Yarrow.htm

This is Yarrow, and you should become friends with her not try to "get rid of her." Remember, who shows up are the right ones. Sit with yarrow, enjoy yarrow's aroma and lovely white flowers, brew tea or beer with yarrow, take heart in knowing should you get cut badly yarrow can help stop the bleeding (Achillea is the genus because Achilles and his men took yarrow into battle with them). Yarrow's also medicine for soil (as all plants who show up tend to be), and is used in biodynamic preps. Whoa yarrow, what an ally!