Wasps in the Ichneumonidae family are parasitic wasps.
The family of Ichneumonidae consists of at least 25,000 species but this is likely to be a very low estimate.
Ichneumonid wasps, with very few exceptions, attack the immature stages of various insects and spiders, eventually killing their hosts.
Adult ichneumonid wasps superficially resemble other wasps. 
They have a slender waist, two pairs of wings, a pair of large compound eyes on the side of the head and three ocelli on top of the head. 
Their size varies considerably from a few millimetres to seven or more centimetres.
Ichneumonid wasps have long antennae (at least 16 segments) and live solitary.
Unfortunately, many species cannot be identified from a photo.

There are quite a few large orange Ichneumonid wasp species in The Netherlands and they are very difficult to tell apart.
For instance, there are several species within the genus Ophion and the genus Netelia.
This may well be an Ophion species, but probably not Ophion luteus, which is usually only seen in July, August and September (my photo was taken in May).

National Park De Biesbosch, The Netherlands, 24 May 2013