A smart contract platform created by Vitalik Buterin in 2015, the world's second-largest cryptocurrency by market cap. • Most blockchain ecosystems (DeFi, NFTs, Layer 2s) are built on Ethereum • Merged from PoW to PoS in 2022, cutting energy consumption by 99% • ETH/BTC ratio gauges alt season — rising ratio = alt strength • More volatile than Bitcoin; tends to show higher returns in bull markets Key Ethereum fundamentals: DeFi TVL (total value locked), gas fees (network usage), and staking ratio.