Quite possibly California’s ultimate day hike! Some choose to make this an overnight trip, but many prefer the simplicity (and light pack weight) of a day hike. The first thing you will need to do is get a permit. Permits can be obtained on recreation.gov. They are available either by the preseason lottery in February. Or leftover permits can be purchased as they become available later in the season. Most people use the Whitney Portal Campground as a base camp due to its elevation and proximity to the trailhead. Because of this, space fills quickly. So it is best to reserve a spot beforehand on recreation.gov.
Although the trail is long and gains LOTS of elevation, it is not technically difficult. All of it could be considered a walk-up. However, the length, elevation gain, and general roughness of the trail can make it a VERY strenuous affair. Proper conditioning is essential to the completion of this hike. Some recommend a VERY early (and even pre-dawn) start to the hike with a strict turnaround time. But this is not absolutely essential unless afternoon thunderstorms are imminent (check the weather forecast).