##Overview
Transaction fees are coins in transactions that are given to miners when the transaction is mined into a block. The transaction fee is given to the miner, which provides an incentive for the miner to place the transaction into a block. There is a non-zero cost associated with including a transaction into a block, due to orphan risk. Infrastructure such as [IBLTs] and [Near Blocks] help reduce the orphan rate on larger blocks, and therefore help reduce the cost of adding a transaction to a block.
Transaction fees establish a way to pick which transactions should go into a block. Transactions with insufficient fees may get stuck on the network, especially when mempools never accept a double spend of the outputs in an unconfirmed transaction. Policies such as [Replace By Fee] and [Child Pays for Parent] can help. Wallets can avoid making destined-to-fail transactions by participating in [Fee Discovery].
Fees are added to transactions by having the sum of the outputs of the transaction be less than the sum of the inputs of the transaction. People have infrequently added absurd transaction fees to a transaction by mistake. The transaction fee cannot be determined by looking at the transaction alone, additional information about the outputs being spent is required. These shortcomings have led to proposals such as [OP_FEE] and [OP_CHECKFEE].
The current block reward is 25 Bitcoins. Eventually, this reward will fall heavily towards 0. With a 0-value block reward, the primary source of income for miners becomes transaction fees. This can lead to issues such as [Fee Sniping] and [Underfunded Mining].
Bogon Fee: A transaction fee that is substantially higher than would would be expected. Example: 50btc when the average total block reward is around 25btc.
CPFP/CP4P: Child Pays For Parent - a child transaction with high fees can incentivize miners to add the unconfirmed parent transaction to a block.
Fee Sniping: Miners try to re-mine the most recent block so that they may steal the fees in the block.
RBF: Replace By Fee - the outputs of an unconfirmed transaction are double-spent in a new transaction with higher miner fees.
##High Signal Links
2015-02-12 - [Replace by fee v0.10.0rc4] (http://lists.linuxfoundation.org/pipermail/bitcoin-dev/2015-February/007404.html)
2013-02-24 - [Fee backlogs discourage fee sniping] (http://lists.linuxfoundation.org/pipermail/bitcoin-dev/2013-February/002186.html)
2013-04-14 - [Funding network security in the future] (https://bitcointalk.org/index.php?topic=176684.0)
2015-05-26 - [First Seen Safe Replace By Fee] (http://lists.linuxfoundation.org/pipermail/bitcoin-dev/2015-May/008248.html)
2014-04-28 - [Replace-by-fee scorched-earth without child-pays-for-parent] (http://lists.linuxfoundation.org/pipermail/bitcoin-dev/2014-April/005620.html)
##Low Signal Links
2015-11-28 - Replace by fee FAQ
2015-06-29 - [Replace by fee deployment schedule] (http://lists.linuxfoundation.org/pipermail/bitcoin-dev/2015-June/009253.html)
2013-10-24 - [Have miners announce their required fees] (http://lists.linuxfoundation.org/pipermail/bitcoin-dev/2013-October/003421.html)
2015-07-11 - [Random block size to facilitate a fee market] (https://bitcointalk.org/index.php?topic=1117914.0)
2014-08-07 - [SIGHASH_ANYONECANPAY extra inputs DoS attack] (http://lists.linuxfoundation.org/pipermail/bitcoin-dev/2014-August/006438.html)
2015-11-23 - [Bogon Fees & Coinbase Forwarding] (http://gnusha.org/bitcoin-wizards/2015-11-23.log)
2015-06-10 - [SPV Fee Discovery mechnaism] (http://lists.linuxfoundation.org/pipermail/bitcoin-dev/2015-June/008549.html)
2014-04-24 - [Replace by fee game theory] (http://lists.linuxfoundation.org/pipermail/bitcoin-dev/2014-April/005504.html)
2013-04-29 - [OP_FEE - explicit transaction fees] (https://bitcointalk.org/index.php?topic=191003.0)
2013-11-22 - [OP_CHECKFEE - an opcode indicating the transaction fee] (so utxo can remain unknown to hardware wallets): https://bitcointalk.org/index.php?topic=343234.0
2013-09-23 - [Near Blocks for Fee Estimation] (http://lists.linuxfoundation.org/pipermail/bitcoin-dev/2013-September/003275.html)
2015-02-12 - [Facing Replace By Fee] (http://sourceforge.net/p/bitcoin/mailman/message/33405247/)
2015-09-04 - [Fee pressure on utxo settling] (http://lists.linuxfoundation.org/pipermail/bitcoin-dev/2015-September/010909.html)
2011-06-06 - [Future fee policy for relaying and mining] (https://bitcointalk.org/index.php?topic=12625.0)
2012-06-15 - [Fee policy for relaying and mining] (http://lists.linuxfoundation.org/pipermail/bitcoin-dev/2012-June/001533.html)
2011-11-07 - [Analysis of Bitcoin Pooled Mining Reward Systems] (https://bitcoil.co.il/pool_analysis.pdf)
2015-05-28 - [Replace by Fee is Harmful] (https://www.reddit.com/r/Bitcoin/comments/30lxo4/replace_by_fee_a_counter_argument_by_mike_hearn/)
2015-06-19 - [F2Pool enabled Full RBF] (https://www.reddit.com/r/Bitcoin/comments/3ae2e1/peter_todd_f2pool_enabled_full_replacebyfee_rbf/)
2015-05-07 - [Block size increase] (http://lists.linuxfoundation.org/pipermail/bitcoin-dev/2015-May/007880.html)
2011-09-25 - [Network-Adjusted transaction fees] (https://bitcointalk.org/index.php?topic=45665.0)
2012-04-25 - [Mine in multiple pools to reduce variance] (https://bitcointalk.org/index.php?topic=78031.0)
2015-06-24 - [Fees are Inevitable] (https://www.reddit.com/r/Bitcoin/comments/3b0593/to_fork_or_not_to_fork/cshphic)
2014-06-09 - [Earn 1% more by mining replace-by-fee] (https://bitcointalk.org/index.php?topic=645120.0)
2015-06-18 - [Replace by Fee Cuts Waste - Reddit Discussion] (https://www.reddit.com/r/Bitcoin/comments/3aawqp/this_is_consensus/csb92so)
David Vorick