Flooring Over Concrete

As we get closer to the DIY season for home improvements, I wanted to go a bit in depth on what products and preparation is necessary to put hard surface flooring over a concrete subfloor.
Product Choices
Having a concrete subfloor does limit the choices you will have for flooring, but there is still a great range of different floors you can put down over concrete.
The best rule here for wood floors is that if it can be installed as a floating floor, than it can be installed over concrete. There are also some floors which can be glued over concrete much as stone and tile floors can be installed over concrete.
Hardwood
Hardwood floor choices to be installed over concrete are typically engineered floors, most of which can be floated. You can also look into engineered or 5/16″ solid floors which can be installed as glue down floors. 3/4″ solid wood floors should NOT be installed over concrete.
Laminate, Bamboo and Cork
For laminate, bamboo and cork all can be installed over concrete, but I suggest looking into the floating choices from these categories as they are far easier to install.
Stone and Tile
Stone and tile can be a great choice to put over concrete subfloors, but a few things should be kept in mind. When installing over concrete it is highly suggested to use an uncoupling layer as this will prevent the tile/stone from getting cracked over time. The reason behind this is that an uncoupling layer absorbs in plane movement as concrete expands and contracts. Without this layer the thinset mortar which holds the tile in place which does not move with the concrete absorbs this movement and cracks occur in the mortar and tile as concrete moves and the tile does not.
Other Flooring Options
There are a few other options out there such as carpet, vinyl and leather tile, and a few select others, but each these flooring types is suited to be laid basically anywhere and there is rarely any installation method which can not be done (most of them are all glued in place).
Subfloor Preparation
Concrete can be very tricky as it is never truly flat, but it is key to make it as flat as possible, so checking how level the floor is and ensuring cracks, and variations in height are taken care of. This is especially true for glue down floors, as variations in subfloor height will telegraph through the floor. Floating floors on the other hand can typically mask variations up to 1/16″ over a span of 8 feet or so, but anything beyond this should have measures taken to level out the subfloor.
Check the moisture level of the subfloor, which should not be higher than 8% moisture content, then you will want to clean the concrete and allow it to dry. Once your concrete is fully dry, do any leveling work necessary, such as grinding down high spots or using a self leveling compound for low spots or filling cracks. Allow any leveling compounds plenty of time to cure and use a concrete sealer if there was more than 8% moisture content in the subfloor.
Installation
Typically when installing over concrete there are only two methods of installation: floating or glue down (you can essentially include using mortar with glue down). Floating installations will be your best bet here as they are far easier to do. When installing a floating floor, ensure that you use a moisture barrier. I would suggest avoiding glue down when possible as they are not only messy, but they are the most likely installation to fail if not done by a professional.
Final Tips
One of the most important parts of the process of installing over concrete is the prep stage and ensuring that your subfloor is ready for installation. The key to any installation is patience and the old saying of measure twice then cut once.