If the soldier you are seeking lost his life in the war there are plenty of resources to help track him down, and between them they may give you a good deal of information that will help in finding more information.
This page is going through a little bit of a rebuild at present. Please forgive the layout and font variations.
The Commonwealth War Graves Commission
See full details of how to search for these records and what they are likely to include at this page.
Assumed deaths
The deaths of many soldiers could only be assumed: see why at this page.
Official registration of death
See full details of the registration records at this page.
Official casualty lists
See full details of the lists and how to find them at this page.
Soldier’s wills
See full details of wills and how to find them at this page.
Soldier’s effects
See details of the way that a man’s effects were dealt with at this page.
See this page for details of unclaimed financial effects.
“Soldiers Died in the Great War”
See details of this useful publication at this page.
Obtaining a photograph of a war grave
See advice on how this can be done at this page.
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Articles on this site
You might find my articles on what happened to a soldier who died and interpreting a cemetery useful in understanding how your soldier came to be buried or commemorated where he is.