I don't think there is any event that fires when you change the Tag on a cell. I'm still not sure I understand the issue, though. If you applicatoin is divided into components that need to know about a change, then why don't you simply fire an event of your own when you change the Tag value of a cell? 

Mike Saltzman"]

Why would need an event? The grid never sets the Tag property on a cell. If it gets set, your code must be setting it. Therefore, you now it was set and don't need an event to tell you so. 

I see your argument about my code being the only one setting the tag value.  But in my case, I can take advantage of event nevertheless. I have my application divided into components that coupled using events. So, when tag value changes, one or more components may be interested. The component setting the tag value does not know (and does not need to know) which components care for the tag value change.

I have considered using the alternate idea of unbound column but this information is on some cells and not on ALL cells. So introducing a column for a cell seems wasteful.

Would you happen to know of a way I can tie such a object to a field in the DataTable. I would like some event to be fire when it that object changed?

 Thanks!

Why would need an event? The grid never sets the Tag property on a cell. If it gets set, your code must be setting it. Therefore, you now it was set and don't need an event to tell you so. 

Another option would be to use an Unbound column in the grid. You can add as many unbound columns to the band as you want to store all the information you need. 

Thanks! If the value of the tag changes, is there any event fired?

If not, is there anything on the cell that would hold the object and fire an event when changed?