Entering unicode characters in linux (gnome)

To directly enter any Unicode character, say ξ, in almost any Gnome application:

1. Find its UTF-16 encoding, for ξ it's 0x03BE (google "ksi unicode")
2. Press CTRL+SHIFT and while holding them enter u03be

Alternative is just to google it, mark, copy and paste.

Very handy for inserting Greek letters in Inkscape and gimp.

Found here.