Many period properties, particularly ones built in the 19th and early 20th century, would originally have had coving/cornicing in all or some of the rooms.
A room without coving looks rather bare – it's amazing what a difference it makes.
As well as being decorative, coving is a good way of hiding hairline cracks and other imperfections, and makes it easier to get a neat line between a different wall and ceiling colour when painting.
Styles of coving changed throughout history, just as styles of architecture did generally, so make sure any coving you buy matches the period of your home.
If you have coving in some rooms and not others, this is the best indication of style, or your neighbours' homes may have original coving you can copy.
Specialist coving companies sell popular period-style designs and can often match existing coving (and repair and restore it, if necessary).
The modern trend of knocking rooms through may mean that you have coving in one half of the room and not the other, which is where matching an original design becomes invaluable.
Period coving is made of plaster and many coving companies also work in plaster. This is fine if they're fitting it for you, but I wouldn't recommend that you put up plaster coving yourself because it's very heavy.
DIYers should play safe and stick to lighter coving materials, which are easier to work with and won't knock you out if they accidentally fall off the ceiling.
The lightest and easier coving to use is expanded polystyrene, but there are other DIY-friendly types, including polyurethane and duropolymer.
As well as getting coving that's the right period for your home, it's important to get the right size for the room.
Large rooms with high ceilings will be able to take wider, more elaborate designs, while smaller rooms with low or standard-height ceilings will be suited to plainer coving.