The iPad uses a special printing technology called AirPrint, that is not compatible with all printers. Even if your printer accepts wireless printing from computers, it is not necessarily compatible with the iPad. This is due to a lack of the software necessary to communicate between the computing device and the printer.
When you use a computer with a printer, you must install software known as a driver that lets the printer and computer communicate, even over a wireless network. Standard printer drivers are not compatible with the iPad's operating system, so AirPrint uses a different system that does not require installing a driver. However, this requires special programming on the printer's end to ensure correct communication, and as of the date of publication, only HP has released printers with the necessary software.
Not all HP printers are AirPrint compatible, but newer ePrint models are more likely than others to work with AirPrint. A selection of both inkjet and laser models work with the iPad, and both black-and-white and color models are supported within each category. When purchasing a printer, whether online or in person, look for the term "AirPrint compatible" or similar wording in the printer's specifications. If you do not see this wording, do not assume the printer will work with the iPad.
The HP Envy EAIO and several models in the LaserJet, PhotoSmart and Officejet series of HP printers are AirPrint compatible. Apple's support website offers a full list of compatible printers, updated periodically as new models become AirPrint-enabled. For some models, you may need to download a firmware update for the printer before it is AirPrint-capable. Follow the instructions that came with your printer to download this update from HP.
Even with the right printer, not all iPad apps support AirPrint. While Apple lets you print from native and internally developed apps, third-party developers are not required to support AirPrint. If you have a specific app you want to print from on your iPad, tap the "Action" button to see your options. If AirPrint is not listed among the choices to which you can send the document, you may need to send it to a different app that supports AirPrint capabilities.