Exchanges, ECNs, dark pools

An equity exchange is a venue where buyers and sellers match orders to trade shares. In 2026 the equity-trading landscape is far more complex than the single-floor New York Stock Exchange of mythology: globally there are dozens of exchanges, hundreds of alternative trading systems, dark pools, and crossing networks. A serious analyst should at least know the major venues, the order-flow rules that govern them, and the differences between exchanges with similar listings.

The major exchanges by market capitalisation

• New York Stock Exchange (NYSE): USD ~28T market cap, anchored by traditional industries and many of the largest US companies.
• NASDAQ: USD ~26T market cap, anchored by technology — Apple, Microsoft, Alphabet, NVIDIA, Amazon, Meta.
• Shanghai Stock Exchange + Shenzhen + Hong Kong: combined Chinese equity universe of USD ~20T.
• Japan Exchange Group (TSE Tokyo + Osaka): USD ~6T market cap.
• Euronext (Amsterdam, Paris, Brussels, Lisbon, Dublin, Milan): USD ~6T combined.
• London Stock Exchange Group: USD ~3T including international listings.
• Bombay Stock Exchange + NSE India: USD ~5T combined.
• Johannesburg Stock Exchange (JSE): USD ~1.2T — the largest African market.
• Nairobi Securities Exchange (NSE Kenya): USD ~25B — the second-largest in sub-Saharan Africa after the JSE.

Lit venues, ECNs, and dark pools

Lit venues (exchanges) display order books publicly: every limit order's price and size is visible pre-trade. Electronic Communication Networks (ECNs) are alternative trading systems that operate similarly but typically with thinner spreads and aggressive maker-taker pricing. Dark pools execute orders without pre-trade transparency — trade is reported after execution but pre-trade orders are not displayed. Estimates place 30-40% of US equity volume in dark venues; the lit/dark split varies by jurisdiction.

Why dark pools exist

Large institutional orders — say, selling USD 200 million of Apple stock — would move the market if executed on lit venues all at once. Showing the size leaks information to high-frequency traders and other counterparties who would adjust prices against the order. Dark pools allow institutions to find natural opposites without revealing intent. The trade-off: less liquidity discovery and the worry that some dark venues have not always served their stated function.

Maker-taker fees and order routing

Many US exchanges charge a 'taker fee' (a few tenths of a basis point) for orders that hit existing limit orders (taking liquidity), and pay a 'maker rebate' (smaller) for limit orders that wait in the book providing liquidity. This structure incentivises HFT firms to constantly post limit orders, capturing the maker rebate. Critics argue the structure incentivises order routing away from the best price toward the highest rebate. The SEC has periodically reviewed the practice but has not banned it.

Best execution and Reg NMS

Under Reg NMS (Regulation National Market System, 2005), US brokers must route orders to whichever venue is showing the best displayed price — the 'order protection rule'. The principle: investors should receive the best execution available across all lit venues. The implementation has become extremely complex with the proliferation of venues and ECNs. The MiFID II equivalent in Europe (best execution) is similar in spirit and similarly complex in practice.

The NSE Kenya in detail

The Nairobi Securities Exchange operates a single lit order book with continuous trading from 9:00 to 15:00 EAT. The market is concentrated: Safaricom alone often accounts for 50-70% of daily turnover; Equity Bank, KCB, EABL, and Bamburi Cement add most of the rest. Foreign-investor participation typically runs 40-65% of daily turnover, making the market sensitive to global risk-on / risk-off shifts and to currency moves.

The NSE has invested in upgrading its trading infrastructure (the Automated Trading System and Central Depository System) and is connected through pan-African initiatives like the African Exchanges Linkage Project. Liquidity remains the principal challenge: average daily turnover is in the range of USD 5-15 million, an order of magnitude below the JSE.