This largely depends on the application and final effect wanted, but an easy way is double sided sticky tape.

It is also possible to fix our standard product using water. It is not adhesive, but an experienced gaffer may be able to ensure that this holds in position, using the following method.

• Clean glass / window thoroughly
• mix tiny amount of detergent (washing up liquid) with water in a spray bottle
• spray glass / window with mixture
• apply lighting filter to glass / window
• use a rubber window wiper to squeeze excess liquid out

It is difficult to recommend a glue. We have tried many and have not found one we could recommend. Many glues solvents that attack the coating on Lighting Filters. This damages them.  

If you need to try a glue we would suggest you try a water based one.  It does depend on how permanent you want the join to be. Please try a small area first.  Please also follow the glue manufacturer's instructions.