Conifer

Something has happened to stress it. Is it in a pot? Its prob rootbound, malnourished and arid. If its in the ground something has changed in its environment. Is a newer plant or tree overshadowing it? Has it become short of light or water. Have you dug through a root? I dont know where in the world you are - it might be useful to speak to a local nursery man or parks dept to see it there is a specific malady affecting conifers locally.

The brown bits will not become green again even if the conifer can be rescued. If it was a central, architectural specimen you could try cutting out the spoilt branches - but you may not like the result.

Good luck

Ann