Symbolism, as a type and movement in poetry, emphasized non-structured "internalized" poetry that, for lack of better words, describe thoughts and feelings in disconnected ways and places, logic, formal structure, and descriptive reality in the back seat. Their models were Charles Baudelaire, Ahmet Haşim, and Walt Whitman; they in turn were models for 20th century "modernist" poets such as Ezra Pound, T S Eliot, and the French Surrealists.
Symbolistpoets tried to capture sensations and states of mind that lay beyond normal consciousness by disordering their senses, indulging in decadence, occultism, and opposition to sober bourgeois values.
The wider concerns of the Symbolists alienation from big business and materialism, the Cartesian split between mind and body, the biological association of thought and feeling are not only pursued by contemporary writers and poets but by scientists and philosophers.
Good introductions to Symbolist literature are: The Symbolist Movement (1970) by W.K. Cornell, The Heritage of Symbolism (1943) by C.M. Bowra and The Symbolist Movement in the Literature of European Languages edited by A. Balakian (1982).