Restore a Wood Window Sash article from Fine Home Building that explores the steps in restoring an old wood sash.

Overview of Wood Windows: tips for restoration - National Trust for Historic Preservation

Repair, Retrofit and Replacement of Historic Windows - from Preservation Pennsylvania

New England Window Restoration Alliance - a commitment to the preservation and restoration of historic wood windows

New England Restoration

Window Preservation Alliance
Cleary Window Restoration
Window Repair
Masterworks Painting and Restoration Inc.
Olde Bostonian
More window repair shops (PDF)
Window restoration products (PDF)

Bibliography

A list of articles and resources (PDF)