Anyone with access to the internet and suitable hardware can participate in mining. In the earliest days of Bitcoin, mining was done with CPUs from normal desktop computers. Graphics cards, or graphics processing units (GPUs), are more effective at mining than CPUs and as Bitcoin gained popularity, GPUs became dominant. Eventually, hardware known as an ASIC (which stands for Application-Specific Integrated Circuit) was designed specifically for mining Bitcoin. The first ones were released in 2013 and have been improved upon since, with more efficient designs coming to market. Today, mining is so competitive, it can only be done profitably with the latest ASICs. When using CPUs, GPUs, or even the older ASICs, the cost of energy consumption is greater than the revenue generated.
As ASICs are advanced and more participants enter the mining space, the difficulty has shot up exponentially. A lot of this activity has been incentivized by the large price increase Bitcoin experienced in 2013 and speculation that the price may rise further. There is also political power within the Bitcoin ecosystem that comes with controlling mining power, since that mining power essentially gives you a vote in whether to accept changes to the protocol.
There are many companies which make mining hardware. Some of the more prominent ones are Bitfury, HashFast, KnCMine