Coinbase is probably the easiest and safest way to purchase bitcoins in the U.S. Unlike BitStamp, Coinbase is not an exchange. They act as a counter-party to all customer trades, you buy or sell your bitcoins directly to Coinbase. The buy/sell fee is 1% on top of the buy/sell spread. The bid/ask is usually close to BitStamp where the firm gets its liquidity from. For example, the current bid is at $635.48 and the current ask is $638.07. In addition to this, the firm has daily limits on the amount of bitcoins bought/sold. These limits are not applied on the individual level. Basically Coinbase has a set amount of bitcoins that it is willing to buy or sell every day. During times or high volatility, users may not be able to buy/sell bitcoins until Coinbase decides to ‘’refill’’ their stock. Here’s a good explanation on this issue from their Customer Support:
Darknet markets present challenges in regard to legality. Bitcoins and other forms of cryptocurrency used in dark markets are not clearly or legally classified in almost all parts of the world. In the U.S., bitcoins are labelled as "virtual assets". This type of ambiguous classification puts pressure on law enforcement agencies around the world to adapt to the shifting drug trade of dark markets.[76]
Researchers have pointed out at a "trend towards centralization". Although bitcoin can be sent directly to the bitcoin network, in practice intermediaries are widely used.[31]:220–222 Bitcoin miners join large mining pools to minimize the variance of their income.[31]:215, 219–222[108]:3[109] Because transactions on the network are confirmed by miners, decentralization of the network requires that no single miner or mining pool obtains 51% of the hashing power, which would allow them to double-spend coins, prevent certain transactions from being verified and prevent other miners from earning income.[110] As of 2013 just six mining pools controlled 75% of overall bitcoin hashing power.[110] In 2014 mining pool obtained 51% hashing power which raised significant controversies about the safety of the network. The pool has voluntarily capped their hashing power at 39.99% and requested other pools to act responsibly for the benefit of the whole network.[111]

Full clients verify transactions directly by downloading a full copy of the blockchain (over 150 GB As of January 2018).[91] They are the most secure and reliable way of using the network, as trust in external parties is not required. Full clients check the validity of mined blocks, preventing them from transacting on a chain that breaks or alters network rules.[92] Because of its size and complexity, downloading and verifying the entire blockchain is not suitable for all computing devices.
The idea of cryptocurrencies has been around for a long time. Developers and coders have been seeking the perfect way to implement cryptography into a digital asset since the birth of the internet. The idea is to use cryptography to secure all transactions of the specific digital asset, as well as control the creation of that same asset through the same means.

Legal Gray Area. Major governments have largely remained on the sidelines, and this has created both a sense of potential and apprehension for Bitcoin proponents and critics respectively. Bitcoin isn’t backed by a regulatory agency and a government would technically be ceding power by supporting a decentralized currency. This has been largely officially unaddressed. Bitcoin’s price, however, tends to be very sensitive to any news concerning the US government’s opinion of cryptocurrencies. For example, when the SEC denied the approval of bitcoin-based exchange-traded-products—essentially bitcoin-backed assets on the stock market—in 2017, Bitcoin’s price dropped 18%. Yet while the price and adoption of Bitcoin would be affected by government action, governments are unable to criminalize Bitcoin. In fact, governments such as the United States and China have invested in it at some capacity.
Transactions are defined using a Forth-like scripting language.[3]:ch. 5 Transactions consist of one or more inputs and one or more outputs. When a user sends bitcoins, the user designates each address and the amount of bitcoin being sent to that address in an output. To prevent double spending, each input must refer to a previous unspent output in the blockchain.[68] The use of multiple inputs corresponds to the use of multiple coins in a cash transaction. Since transactions can have multiple outputs, users can send bitcoins to multiple recipients in one transaction. As in a cash transaction, the sum of inputs (coins used to pay) can exceed the intended sum of payments. In such a case, an additional output is used, returning the change back to the payer.[68] Any input satoshis not accounted for in the transaction outputs become the transaction fee.[68]
Bitcoin is a digital currency, also known as a cryptocurrency, and is created or mined when people solve complex math puzzles online. These bitcoins are then stored in a digital wallet that exists on the cloud or the user’s computer. Because bitcoins are not housed in bank accounts, brokerage, or futures accounts, they are not insured by the FDIC or SIPC.
We recommend you to cross check Bitcoin exchanges with their local government authorities, before signing in. Do check whether the Bitcoin Exchange is fully complied with the regulations and whether they are regulated or not; also check whether it has been involved in any malicious and unethical activity before or not. You may also choose to read independent reviews, available online before making any decision. We recommend
Though transaction fees are optional, miners can choose which transactions to process and prioritize those that pay higher fees.[68] Miners may choose transactions based on the fee paid relative to their storage size, not the absolute amount of money paid as a fee. These fees are generally measured in satoshis per byte (sat/b). The size of transactions is dependent on the number of inputs used to create the transaction, and the number of outputs.[3]:ch. 8
Sadly, with the demise of Cryptsy there is a need for a new major first-rate cryptocurrency and Bitcoin exchange (aka altcoins). Having many medium-sized cryptocurrency exchange bitcoin sites is a better situation than having one large amazing option. Bittrex (new account creation temporarily disabled) has now replaced Poloniex as the largest most amazing option to exchange bitcoin. Its platform is functional enough to have attracted tens of millions of new customer every month. Things feel smooth when using Bittrex. All big and small trading pairs are offered and it is now possible to do cryptocurrency margin trading on major altcoins. This is a cool feature, but use it with caution as leveraged trading has a certain risk factor. Keep in mind that some of the best bitcoin exchange sites also do altcoins. Yobit, Bittrex, Cryptopia and Changelly, are great options worth checking out. Some even offer short selling on major coins.
The silence of the Chinese authorities was seen as a subtle acceptance signal by market participants. The situation didn’t last long however. On December 7th, The People’s Bank of China barred financial institutions from buying or selling virtual currency or Bitcoin related products. The Bank also demanded that businesses stop with the practice of pricing their products in Bitcoins. BTC/USD opened the day at $906.50 on BTC-E. After the news hit the wires, bitcoin prices crashed from to a low of $551 in only 9 hours, a fall of 39%.
The current cryptocurrency market is estimated to be worth around $148 billion, but analysts believe that figure could climb to a staggering $1 trillion by 2019. This makes day trading bitcoin in 2017 an appealing proposition. Bitcoin makes up half of the cryptocurrency market and Roger Ver, Bitcoins CEO, believes ‘it’s the dawn of a better, more free world’. Whilst that remains to be seen, it does have certain attributes that make it tempting for those looking to make money day trading bitcoin.
In the blockchain, bitcoins are registered to bitcoin addresses. Creating a bitcoin address requires nothing more than picking a random valid private key and computing the corresponding bitcoin address. This computation can be done in a split second. But the reverse, computing the private key of a given bitcoin address, is mathematically unfeasible. Users can tell others or make public a bitcoin address without compromising its corresponding private key. Moreover, the number of valid private keys is so vast that it is extremely unlikely someone will compute a key-pair that is already in use and has funds. The vast number of valid private keys makes it unfeasible that brute force could be used to compromise a private key. To be able to spend their bitcoins, the owner must know the corresponding private key and digitally sign the transaction. The network verifies the signature using the public key.[3]:ch. 5