Cardano's ADA cryptocurrency can be purchased on a variety of cryptocurrency exchanges and platforms. Some of the popular platforms where you can buy Cardano ADA include:

1. Binance: Binance is one of the largest and most well-known cryptocurrency exchanges in the world. It offers a wide range of trading pairs, including ADA/BTC and ADA/USDT.

2. Coinbase: Coinbase is a user-friendly platform that is popular among beginners. It allows users to buy, sell, and store ADA directly on the platform.

3. Kraken: Kraken is a reputable exchange with a strong focus on security and regulatory compliance. It offers ADA trading pairs and supports fiat currency deposits.

4. Bittrex: Bittrex is another popular cryptocurrency exchange that supports ADA trading pairs. It offers a simple and intuitive interface for buying and selling ADA.

5. Huobi: Huobi is a global exchange that offers ADA trading pairs and a variety of other cryptocurrencies. It is known for its liquidity and competitive trading fees.

When choosing a platform to buy Cardano ADA, it's important to consider factors such as security, fees, user interface, and supported trading pairs. Additionally, make sure to use platforms that are reputable and have a good track record of customer service. Remember to store your ADA in a secure wallet to protect your investment.