LAANC is the Low Altitude Authorization and Notification Capability. It is the fast way for a Part 107 remote pilot to get prior air traffic control authorization to fly in controlled airspace. Section 107.41 requires that authorization before you operate in Class B, Class C, Class D, or within the lateral boundaries of Class E airspace designated for an airport surface area. LAANC checks the request against the UAS Facility Maps and can return an approval in near real time, up to the altitude published for that grid.
It is the fastest common method. Mailing a form and waiting a year is not. Filing an IFR flight plan is not. Calling the tower as you unfold the arms is not "prior" authorization.
Read the name the way the test uses it. Low altitude means the approval stays inside the published grid and inside the 400-foot rule. It is not automatic approval to fly above 400 feet anywhere in the National Airspace System. Notification is not a flight plan you file after you are airborne. The capability is the automated check against the UAS Facility Maps. If an answer says LAANC issues a visual-line-of-sight waiver, or that it issues your remote pilot certificate, that answer is describing a different process. The matching description is near-real-time authorization to operate in controlled airspace, checked against those maps.
What the grid ceiling means
Each grid cell has a ceiling. If you receive a LAANC authorization with a grid ceiling of 200 feet, you may operate up to 200 feet AGL inside that grid. You may not treat 400 feet as automatic because §107.51 allows 400 feet in the absence of a tighter limit. The authorization is the tighter limit. You also may not use one grid's approval to fly "anywhere in the city." The approval is for the airspace and altitude you requested.
LAANC does not authorize flight above 400 feet AGL anywhere. A job that needs more than 400 feet over open terrain, with no structure exception, is a waiver of §107.51 if it can be approved at all. Taking that request to LAANC because the site is under a Class B shelf mixes the two systems. In Class G, LAANC is not even the tool, because §107.41 does not require authorization there. The 400-foot rule still applies.
What LAANC will not do
LAANC does not waive visual line of sight, operations over people, the anti-collision light, or any other Part 107 operating limit. New operational waivers go through the Aviation Safety Hub. The FAA waivers page is the reference for that split. Previously submitted waivers remain in FAADroneZone. FAADroneZone is also where you go for a manual airspace authorization when LAANC does not cover the location or the altitude you need.
LAANC does not issue remote pilot certificates, register aircraft, or grant permission to enter a prohibited or restricted area under §107.45. Those are different permissions. The authorization you can plan on is the one the FAA tool returns for that grid, at or below the published ceiling, for the time window you were given.
How this shows up on a site
Read the chart first, using the airspace classes page. If you are inside Class B, C, D, or surface Class E, you need authorization before launch. Open LAANC, request the grid, and read the ceiling you were given. If the job needs 300 feet and the grid offers 100, the manual FAADroneZone process is the alternative, not a decision to fly the mission anyway. If the chart shows Class G under a 700-foot Class E floor, you do not use LAANC to "get permission" for a 200-foot roof. You still comply with visibility, clouds, altitude, and see-and-avoid.
Check NOTAMs after the authorization. A LAANC approval does not cancel a temporary flight restriction. And check the time. An approval for a morning window is not an approval for a reshoot at dusk, especially if dusk becomes a night operation with its own lighting and training rules.