Trading on margin or using a margin loan involves taking a loan using your existing shares as security. The borrowed funds are then used to buy more shares. Each organisation has borrowing rules, but generally will let you borrow between 40% to 70% of the value of the shares. For example, if you had $10000 to invest and geared the purchase with a margin loan, you could borrow $20000 to give you a portfolio of $30000 (this is borrowing 66% of the portfolio). The benefits are increasing your return and a tax deduction against the interest expense, while the main disadvantage is that the loan can magnify your losses. More information on margin lending is available from your institution.