Python-SQL queries with variables

I am having problems when I run a query to return the information of the students, I get this error:

File "I:\A2\SQLite\Create Table.py", line 140, in searchStudent cur.execute("SELECT Student_ID, First_Name, Last_Name FROM School WHERE First_Name IS "+firstName) sqlite3.OperationalError: no such column: Joshua

Here is the code, Joshua was the input for the name.

    firstName = input("\nWhat is the first name of the student you would like to search for?")

    con = sqlite3.connect("School.sql")
    cur = con.cursor()

    cur.execute("SELECT Student_ID, First_Name, Last_Name FROM School WHERE First_Name IS "+firstName)

    print(cur.fetchall())

The database has 30 entries, holding the Student_ID (primary key), First_Name (text), Last_Name (text), Year (integer), Form_Group(text) and House(text).

The query should return the details of all students with the same first name. This should include their Student_ID, First_Name and Last_Name.

What is causing the error?

Edit: I tried:

    WHERE First_Name = "+firstName

But that brought the same error.