Insects in the family Tettigoniidae are commonly called Katydids or Bush-crickets.
There are more than 6,400 species.
They are also known as Long-horned Grasshoppers, although they are more closely related to crickets than to any type of grasshopper.

1st & 2nd photo: A female. 's Graveland, The Netherlands, 12 August 2011
3rd photo: A male. Zanderij Crailo, Hilversum, The Netherlands, 29 August 2013
4th photo: A male nymph. Zanderij Crailo, Hilversum, The Netherlands, 24 June 2013
5th photo: A female nymph. Zanderij Crailo, Hilversum, The Netherlands, 24 June 2013