The Romantic period is generally thought to have begun in the late 18th century and continued into the first third of the 19th century. More specifically, it's thought to have started around 1789 and lasted until 1832. Some of Romanticism's most famous authors include William Wordsworth, Samuel Taylor Coleridge, John Keats, Mary Wollstonecraft Shelley, Lord Byron, and Percy Bysshe Shelley.
The interior experience of the individual is one of the most important characteristics of Romantic literature. Rejecting rigid social, religious, and political traditions, the Romantics emphasized the subjective experience of the individual, arguing that feelings or emotions should be prized over logic. As such, much of Romantic literature presents us with radically isolated individuals who have rejected conventional society. Additionally, Romantic literature is often associated with the natural world and nature, and a great deal of Romantic poetry involves lengthy descriptions of expansive, natural vistas. That said, it would be a mistake to simply characterize the Romantics as "nature" poets. Indeed, most Romantic writers did not write about nature in order to focus solely on the natural world, but rather to introduce and explore a more abstract theme. Often, this theme explored the status of the individual's interior, and so the natural world often served as a starting point for the author's discussion of the state of the individual and the interior self.
It might help to check out a sample poem to see how these ideas work in real time. The poem below (Wordsworth's "The World Is Too Much With Us") illustrates many prominent Romantic themes, such as the rejection of conventional society, descriptions of nature, and a presentation of a radically individualistic self.
The world is too much with us; late and soon,
Getting and spending, we lay waste our powers;—
Little we see in Nature that is ours;
We have given our hearts away, a sordid boon!
This Sea that bares her bosom to the moon;
The winds that will be howling at all hours,
And are up-gathered now like sleeping flowers;
For this, for everything, we are out of tune;
It moves us not. Great God! I’d rather be
A Pagan suckled in a creed outworn;
So might I, standing on this pleasant lea,
Have glimpses that would make me less forlorn;
Have sight of Proteus rising from the sea;
Or hear old Triton blow his wreathèd horn.